Light-emitting element, light-emitting device, electronic device, and lighting device

ABSTRACT

Provided is a novel light-emitting element and a light-emitting element with high light emission efficiency. A light-emitting element at least includes a first electrode, a first light-emitting layer over the first electrode, a second light-emitting layer over and in contact with the first light-emitting layer, a third light-emitting layer over and in contact with the first light-emitting layer, and a second electrode over the third light-emitting layer. One of the first light-emitting layer and the second light-emitting layer contains at least a green-light-emitting phosphorescent compound. The other of the first light-emitting layer and the second light-emitting layer contains at least an orange-light-emitting phosphorescent compound. The third light-emitting layer contains at least a blue-light-emitting hole-trapping fluorescent compound and an organic electron-transport compound that disperses the fluorescent compound.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to, for example, a semiconductor device, adisplay device, a light-emitting device, a power storage device, adriving method thereof, or a manufacturing method thereof. Inparticular, one embodiment of the present invention relates to alight-emitting element and a light-emitting device using anelectroluminescence (EL) phenomenon, and an electronic device and alighting device using the light-emitting element and the light-emittingdevice.

2. Description of the Related Art

In recent years, research and development have been extensivelyconducted on light-emitting elements utilizing the EL phenomenon. In abasic structure of such a light-emitting element, a layer containing alight-emitting organic compound (hereinafter also referred to as an ELlayer) is sandwiched between a pair of electrodes. The light-emittingelement utilizing the EL phenomenon has attracted attention as anext-generation flat panel display element owing to characteristics suchas feasibility of being thinner and lighter, high-speed response toinput signals, and capability of direct current low voltage driving. Inaddition, a display using such the light-emitting element has a featurethat it is excellent in contrast and image quality, and has a wideviewing angle. Further, since such a light-emitting element is a planelight source, application of the light-emitting element as a lightsource such as a backlight of a liquid crystal display and anillumination device is proposed.

In the case of a light-emitting element in which a layer containing anorganic compound used as a light-emitting substance is provided betweena pair of electrodes, by applying a voltage to the element, electronsfrom a cathode and holes from an anode are injected into the layercontaining the organic compound and thus a current flows. The injectedelectrons and holes then lead the organic compound to its excited state,so that light emission is obtained from the excited organic compound.

As the excited state caused by an organic compound, there are a singletexcited state (S*) and a triplet excited state (T*). Light emissiongenerated in a singlet excited state is referred to as fluorescence andlight emission generated in a triplet excited state is referred to asphosphorescence. Here, in a compound that emits fluorescence(hereinafter also referred to as a fluorescent compound), in general,phosphorescence is not observed at room temperature, and onlyfluorescence is observed. Accordingly, the internal quantum efficiency(the ratio of generated photons to injected carriers) of alight-emitting element including the fluorescent compound is assumed tohave a theoretical limit of 25% based on the ratio of the singletexcited state to the triplet excited state.

On the other hand, when a compound that emits phosphorescence(hereinafter also referred to as a phosphorescent compound) is used, theinternal quantum efficiency can be theoretically increased to 100%. Thatis, higher emission efficiency can be obtained than using a fluorescentcompound. For these reasons, a light-emitting element including aphosphorescent compound has been actively developed in recent years inorder to obtain a light-emitting element with high emission efficiency.

As the phosphorescent compound, an organometallic complex that hasiridium or the like as a central metal have particularly attractedattention because of their high phosphorescence quantum yield; forexample, an organometallic complex that has iridium as a central metalis disclosed as a phosphorescent material in Patent Document 1.

REFERENCE Patent Document

-   [Patent Document 1] PCT International Publication No. 00/70655

SUMMARY OF THE INVENTION

Development of a light-emitting element using a phosphorescent compoundstill leaves room for improvement in terms of emission efficiency,reliability, cost, and the like. Thus, improvement of an elementstructure, development of a substance, and the like are being carriedout.

An object of one embodiment of the present invention is to provide anovel light-emitting element. Another object of one embodiment of thepresent invention is to provide a novel light-emitting device. Anotherobject of one embodiment of the present invention is to provide a novelelectronic device or a novel lighting device.

Another object of one embodiment of the present invention is to providea light-emitting element with high emission efficiency. Another objectof one embodiment of the present invention is to provide alight-emitting device with high emission efficiency. Another object ofone embodiment of the present invention is to provide an electronicdevice or a lighting device with low power consumption. Another objectof one embodiment of the present invention is to provide alight-emitting element or the like with a long lifetime. Another objectof one embodiment of the present invention is to provide alight-emitting element or the like with high reliability. Another objectof one embodiment of the present invention is to provide a non-breakablelight-emitting device or the like. Another object of one embodiment ofthe present invention is to provide a flexible light-emitting device orthe like. Another object of one embodiment of the present invention isto provide a light-emitting device or the like with high lightextraction efficiency. Another object of one embodiment of the presentinvention is to provide a lightweight light-emitting device or the like.

Note that the descriptions of these problems do not disturb theexistence of other problems. Note that in one embodiment of the presentinvention, there is no need to achieve all of the objects. Other objectswill be apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

One embodiment of the present invention is a light-emitting element atleast including a first electrode, a first light-emitting layer over thefirst electrode, a second light-emitting layer over and in contact withthe first light-emitting layer, a third light-emitting layer over and incontact with the first light-emitting layer, and a second electrode overthe third light-emitting layer. One of the first light-emitting layerand the second light-emitting layer contains at least agreen-light-emitting phosphorescent compound. The other of the firstlight-emitting layer and the second light-emitting layer contains atleast an orange-light-emitting phosphorescent compound. The thirdlight-emitting layer contains at least a blue-light-emittinghole-trapping fluorescent compound (which easily accepts holes) and anelectron-transport compound that disperses the fluorescent compound.

In the light-emitting element, one of the first light-emitting layer andthe second light-emitting layer preferably contains a first organiccompound that disperses the green-light-emitting phosphorescentcompound. In the light-emitting element, the other of the firstlight-emitting layer and the second light-emitting layer preferablycontains a second organic compound that disperses theorange-light-emitting phosphorescent compound. In particular, the firstorganic compound is preferably the same as the second organic compound.

Note that in this specification, the maximum emission wavelength of thegreen-light-emitting phosphorescent compound is greater than 500 nm andless than or equal to 570 nm, the maximum emission wavelength of theorange-light-emitting phosphorescent compound is greater than 570 nm andless than or equal to 620 nm, and the maximum emission wavelength of theblue-light-emitting hole-trapping fluorescent compound is less than orequal to 500 nm (note that this wavelength is included in visible lightrange, e.g., greater than or equal to 400 nm).

Further, in the light-emitting element, the blue-light-emittinghole-trapping fluorescent compound preferably contains a pyreneskeleton. Further, in the light-emitting element, the electron-transportcompound that disperses the fluorescent compound preferably contains ananthracene skeleton.

Another embodiment of the present invention is a light-emitting deviceincluding the above-described light-emitting element. Another embodimentof the present invention is an electronic device including thelight-emitting device in a display portion. Another embodiment of thepresent invention is a lighting device including the light-emittingdevice in a light-emitting portion.

Note that the light-emitting device in this specification includes animage display device that uses a light-emitting element. Further, thecategory of the light-emitting device in this specification includes amodule in which a light-emitting element is provided with a connectorsuch as an anisotropic conductive film or a TCP (tape carrier package);a module in which the top of the TCP is provided with a printed wiringboard; and a module in which an IC (integrated circuit) is directlymounted on a light-emitting element by a COG (chip on glass) method.Furthermore, light-emitting devices that are used in lighting equipmentand the like shall also be included.

According to another embodiment of the present invention, a novellight-emitting element can be provided. According to one embodiment ofthe present invention, a novel light-emitting device can be provided.According to one embodiment of the present invention, a novel electronicdevice or a novel lighting device can be provided.

According to one embodiment of the present invention, a light-emittingelement having high emission efficiency can be provided. According toone embodiment of the present invention, a light-emitting device withhigh emission efficiency can be provided. According to one embodiment ofthe present invention, an electronic device or a lighting device withlow power consumption can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D each illustrate an example of a light-emitting element ofone embodiment of the present invention.

FIG. 2 illustrates an example of a light-emitting device of oneembodiment of the present invention.

FIGS. 3A and 3B each illustrate an example of a light-emitting device ofone embodiment of the present invention.

FIGS. 4A to 4E illustrate an example of a method for manufacturing alight-emitting device of one embodiment of the present invention.

FIGS. 5A to 5E illustrate an example of a method for manufacturing alight-emitting device of one embodiment of the present invention.

FIGS. 6A and 6B illustrate an example of a light-emitting device of oneembodiment of the present invention.

FIGS. 7A and 7B illustrate an example of a light-emitting device of oneembodiment of the present invention.

FIGS. 8A to 8E illustrate examples of an electronic device of oneembodiment of the present invention.

FIGS. 9A and 9B illustrate an example of a lighting device of oneembodiment of the present invention.

FIGS. 10A to 10D illustrate light-emitting devices in Example 1 andExample 2.

FIGS. 11A and 11B illustrate a light-emitting device in Example 1.

FIG. 12 shows results of a reliability test.

FIG. 13 shows measurement results of reflectivity of an electrode.

FIG. 14 shows measurement results of temperature characteristics.

FIGS. 15A and 15B show measurement results of temperature distributionon a surface of a light-emitting element.

FIGS. 16A and 16B illustrate a light-emitting device of Example 2.

FIG. 17 shows results of a reliability test.

FIGS. 18A to 18D each illustrate a light emitting element in Examples 1to 3.

FIGS. 19A to 19C are STEM (Scanning Transmission Electron Microscopy)images of samples according to Example 4.

FIG. 20 shows measurement results of stress values of Example 5.

FIG. 21 illustrates a light-emitting device of Example 6.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the invention is not limited to the following description, andit will be easily understood by those skilled in the art that variouschanges and modifications can be made without departing from the spiritand scope of the invention. Therefore, the invention should not beconstrued as being limited to the description in the followingembodiments. Note that in the structures of the invention describedbelow, the same portions or portions having similar functions aredenoted by the same reference numerals in different drawings, anddescription of such portions is not repeated.

(Embodiment 1)

In Embodiment 1, light-emitting elements of embodiment of the presentinvention will be described with reference to FIGS. 1A to 1D.

<Structure of Light-Emitting Element>

A light-emitting element of one embodiment of the present invention atleast includes a first electrode, a first light-emitting layer over thefirst electrode, a second light-emitting layer over and in contact withthe first light-emitting layer, a third light-emitting layer over and incontact with the first light-emitting layer, and a second electrode overthe third light-emitting layer. One of the first light-emitting layerand the second light-emitting layer contains at least agreen-light-emitting phosphorescent compound. The other of the firstlight-emitting layer and the second light-emitting layer contains atleast an orange-light-emitting phosphorescent compound. The thirdlight-emitting layer contains at least a blue-light-emittinghole-trapping fluorescent compound (which easily accepts holes) and anelectron-transport compound that disperses the fluorescent compound.

In the light-emitting element of one embodiment of the presentinvention, the green-light-emitting phosphorescent compound, theorange-light-emitting phosphorescent compound, and theblue-light-emitting fluorescent compound are used as light-emittingsubstances. Adjustment of emission balance among the phosphorescent andfluorescent light-emitting layers can increase emission efficiency ofthe light-emitting element.

In the light-emitting element of one embodiment of the presentinvention, the electron-transport organic compound is used as a hostmaterial of the blue-light-emitting fluorescent compound and ispositioned to be the closest to the cathode among the threelight-emitting layers; with this structure, light emission from thephosphorescent compounds is easily obtained. Accordingly, thelight-emitting element with high emission efficiency is achieved.

Although light emitted from a fluorescent compound is weaker than thatfrom a phosphorescent compound, one embodiment of the present inventionis preferable particularly in the case where a strong blue emission isunnecessary and high emission efficiency is required, for example, for awarm-white light-emitting device used as lighting.

In order to obtain a highly efficient light-emitting element, thefollowing have been proposed: a tandem light-emitting element in which aplurality of EL layers is stacked with a charge generation regionsandwiched therebetween, and a light-emitting element whoselight-emitting substances are all phosphorescent compounds. The kind andthe number of films included in the light-emitting element of oneembodiment of the present invention are less than those of a tandemlight-emitting element. Therefore, a highly efficient light-emittingelement can be manufactured in a short manufacturing process at lowcost. In addition, the lifetime of a blue-light-emitting fluorescentcompound is longer than that of a blue-light-emitting phosphorescentcompound; thus, a highly reliable light-emitting element can be achievedin one embodiment of the present invention.

A light-emitting element shown in FIG. 1A includes a first electrode101, an EL layer 103 over the first electrode 101, and a secondelectrode 105 over the EL layer 103. In this embodiment, the firstelectrode 101 serves as an anode, and the second electrode 105 serves asa cathode.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the first electrode 101 and the secondelectrode 105, holes are injected to the EL layer 103 from the firstelectrode 101 side and electrons are injected to the EL layer 103 fromthe second electrode 105 side. The injected electrons and holes arerecombined in the EL layer 103 and a light-emitting substance containedin the EL layer 103 emits light.

The EL layer 103 includes a first light-emitting layer 203 a, a secondlight-emitting layer 203 b over and in contact with the firstlight-emitting layer 203 a, and a third light-emitting layer 203 c overand in contact with the second light-emitting layer 203 b. One of thefirst light-emitting layer 203 a and the second light-emitting layer 203b contains a green-light-emitting phosphorescent compound, and the otherthereof contains an orange-light-emitting phosphorescent compound. Thethird light-emitting layer 203 c contains a blue-light-emittinghole-trapping fluorescent compound and an electron-transport compoundwhich disperses the fluorescent compound. Either a low molecularcompound or a high molecular compound can be used for the EL layer 103,and an inorganic compound may also be contained.

The EL layer 103 may further include, as a layer other than thelight-emitting layers, a layer containing a hole-injection substance oran electron-injection substance, a hole-transport substance or anelectron-transport substance, a bipolar substance (i.e., a substance inwhich the electron-transport property and the hole-transport propertyare high), and the like.

A light-emitting element shown in FIG. 1B includes a hole-injectionlayer 201 over the first electrode 101 and between the first electrode101 and the first light-emitting layer 203 a, and a hole-transport layer202 over the hole-injection layer 201. Further, an electron-transportlayer 204 over and in contact with the third light-emitting layer 203 c,and an electron-injection layer 205 over and in contact with theelectron-transport layer 204 are included between the thirdlight-emitting layer 203 c and the second electrode 105. Note that thefirst light-emitting layer 203 a, the second light-emitting layer 203 b,and the third light-emitting layer 203 c contain materials similar tothose in FIG. 1A.

A light-emitting element shown in FIG. 1C includes the first electrode101, the EL layer 103 over the first electrode 101, an interlayer 107over the EL layer 103, and the second electrode 105 over the interlayer107. The EL layer 103 has the same structure as that in FIG. 1A.

A specific example of the structure of the interlayer 107 is shown inFIG. 1D. The interlayer 107 includes at least a charge generation region208 that is in contact with the second electrode 105. In addition to thecharge-generation region 208, the interlayer 107 may further include anelectron-relay layer 207 and an electron-injection buffer layer 206.

A light-emitting element shown in FIG. 1D includes the first electrode101, the EL layer 103 over the first electrode 101, the interlayer 107over the EL layer 103, and the second electrode 105 over the interlayer107. The interlayer 107 includes the electron-injection buffer layer206, the electron-relay layer 207 over the electron-injection bufferlayer 206, and the charge generation region 208 over the electron-relaylayer 207 and in contact with the second electrode 105. The structure ofthe EL layer 103 is the same as that of FIG. 1A.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the first electrode 101 and the secondelectrode 105, holes and electrons are generated in thecharge-generation region 208, and the holes move into the secondelectrode 105 and the electrons move into the electron-relay layer 207.The electron-relay layer 207 has a high electron-transport property andimmediately transfers the electrons generated in the charge-generationregion 208 to the electron-injection buffer layer 206. Theelectron-injection buffer layer 206 reduces a barrier against electroninjection into the EL layer 103, so that the efficiency of the electroninjection into the EL layer 103 can be improved. Thus, the electronsgenerated in the charge-generation region 208 are injected into thelowest unoccupied molecular orbital (LUMO) level of the EL layer 103through the electron-relay layer 207 and the electron-injection bufferlayer 206.

In addition, the electron-relay layer 207 can prevent interaction inwhich the substance included in the first charge generation region 208and the substance included in the electron-injection buffer layer 206react with each other at the interface therebetween to damage thefunctions of the first charge generation region 208 and theelectron-injection buffer layer 206.

<Materials of Light-Emitting Element>

Examples of materials which can be used for each layer will be describedbelow. Note that each layer is not limited to a single layer, but may bea stacked-layer of two or more layers.

<Anode>

The electrode serving as the anode (the first electrode 101 in thisembodiment) can be formed using one or more kinds of conductive metals,alloys, conductive compounds, and the like. In particular, it ispreferable to use a material with a high work function (4.0 eV or more).Examples include indium tin oxide (ITO), indium tin oxide containingsilicon or silicon oxide, indium zinc oxide, indium oxide containingtungsten oxide and zinc oxide, graphene, gold, platinum, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, and anitride of a metal material (e.g., titanium nitride). Alternatively, theelectrode may be formed as follows: silver, copper, aluminum, titanium,or the like is formed to have a nanowire shape (or a thin-stripe shape),and then a conductive substance (a conductive organic material,graphene, or the like) is formed thereover by a coating method, aprinting method, or the like.

When the anode is in contact with the charge-generation region, any of avariety of conductive materials can be used regardless of their workfunctions; for example, aluminum, silver, an alloy containing aluminum,or the like can be used.

<Cathode>

The electrode serving as the cathode (the second electrode 105 in thisembodiment) can be formed using one or more kinds of conductive metalsand alloys, conductive compounds, and the like. In particular, it ispreferable to use a material with a low work function (3.8 eV or less).Examples include aluminum, silver, an element belonging to Group 1 or 2of the periodic table (e.g., an alkali metal such as lithium or cesium,an alkaline earth metal such as calcium or strontium, or magnesium), analloy containing any of these elements (e.g., Mg—Ag or Al—Li), a rareearth metal such as europium or ytterbium, and an alloy containing anyof these rare earth metals.

Note that in the case where the cathode is in contact with thecharge-generation region, a variety of conductive materials can be usedregardless of its work function. For example, ITO, silicon, or indiumtin oxide containing silicon oxide can be used.

The electrodes each can be formed by a vacuum evaporation method or asputtering method. Alternatively, when silver paste or the like is used,a coating method or an inkjet method can be used.

In addition, an insulating film such as an organic film, a transparentsemiconductor film, or a silicon nitride film may be formed over thecathode (also referred to as an upper electrode). These films serve aspassivation films and can suppress the entrance of impurities andmoisture into the light-emitting element, or can reduce loss of lightenergy due to surface plasmon in the cathode.

<Light-Emitting Layer>

As described above, the light-emitting element of one embodiment of thepresent invention includes a light-emitting layer containing agreen-light-emitting phosphorescent compound, a light-emitting layercontaining an orange-light-emitting phosphorescent compound, and alight-emitting layer containing a blue-light-emitting hole-trappingfluorescent compound and an electron-transport compound that dispersesthe fluorescent compound.

The phosphorescent compounds and the fluorescent compound can bereferred to as guest materials in respective light-emitting layers. Theelectron-transport compound that disperses the fluorescent compound canbe referred to as a host material. The light-emitting layer containing agreen-light-emitting phosphorescent compound and the light-emittinglayer containing an orange-light-emitting phosphorescent compound mayeach contain an organic compound that disperses the phosphorescentcompound (host material). Each of the light-emitting layers may furthercontain a material other than the guest material and the host material.

The guest material is preferably dispersed in the host material. Whenthe light-emitting layer has the structure in which the guest materialis dispersed in the host material, the crystallization of thelight-emitting layer can be inhibited. Further, concentration quenchingdue to high concentration of the guest material can be suppressed andthus the light-emitting element can have high emission efficiency. Anelectron-transport compound and a hole-transport compound, which aredescribed below, can be used as the host materials. In particular, anelectron-transport compound is used for the third light-emitting layer203 c.

Note that the T₁ level of the host material (or a material other thanthe guest material in the light-emitting layer) is preferably higherthan the T₁ level of the guest material. This is because, when the T₁level of the host material is lower than that of the guest material, thetriplet excitation energy of the guest material, which is to contributeto light emission, is quenched by the host material and accordingly theemission efficiency is decreased.

Examples of the phosphorescent compound that emits orange light or greenlight include the following: an organometallic iridium complex having apyrimidine skeleton such as(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(mppm)₃]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₃]),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₂(acac)]),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(mpmppm)₂(acac)]), and(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(mixture of endo- and exo-) (abbreviation: [Ir(nbppm)₂(acac)]); anorganometallic iridium complex having a pyrazine skeleton such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]), and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]); an organometallic iridium complexhaving a pyridine skeleton such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),bis[2-phenylpyridinato-N,C^(2′)]iridium(III)acetylacetonate(abbreviation: [Ir(ppy)₂(acac)]),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation:[Ir(bzq)₂(acac)]), tris(benzo[h]quinolinato)iridium(III) (abbreviation:[Ir(bzq)₃]), tris(2-phenylquinolinato-N,C²′)iridium(III) (abbreviation:[Ir(pq)₃]), and bis(2-phenylquinolinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(pq)₂(acac)]); an organometalliciridium complex in which a phenylpyridine derivative having anelectron-withdrawing group is a ligand, such asbis[2-(3′,5′-bistrifluoromethylphenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(abbreviation: Ir(CF₃ ppy)₂(pic)), orbis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III)acetylacetonate (abbreviation: FIracac); and a rare earth metal complexsuch as tris(acetylacetonato) (monophenanthroline)terbium(III)(Tb(acac)₃(Phen)).

Examples of the blue-light-emitting hole-trapping fluorescent compoundincludeN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPrn),N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6 mMemFLPAPrn),N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA). A fluorescent compound having a pyrene skeletonis particularly preferable because of their high hole-trappingproperties, high emission efficiency, and high reliability. In addition,condensed aromatic diamine compounds typified by pyrenediamine compoundssuch as 1,6FLPAPrn and 1,6 mMemFLPAPrn are particularly preferablebecause of their high hole-trapping properties, high emissionefficiency, and high reliability.

As the electron-transport compound, a π-electron deficientheteroaromatic compound such as a nitrogen-containing heteroaromaticcompound, a metal complex having a quinoline skeleton or abenzoquinoline skeleton, a metal complex having an oxazole-based orthiazole-based ligand, or the like can be used.

Specific examples include the following: metal complexes such asbis(10-hydroxybenzo[h]quinolinato)berylium (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato) (4-phenylphenolato)aluminum (abbreviation:BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂), andbis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂);heterocyclic compounds having polyazole skeletons, such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), and2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); heterocyclic compounds having quinoxalineskeletons or dibenzoquinoxaline skeletons, such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 6mDBTPDBq-II), and2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq); heterocyclic compounds having diazineskeletons (pyrimidine skeletons or pyrazine skeletons), such as4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine(abbreviation: 4,6mCzP2 Pm), and4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II); heterocyclic compounds having pyridine skeletons, such as3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 3,5DCzPPy),1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB), and3,3′,5,5′-tetra[(m-pyridyl)-phen-3-yl]biphenyl (abbreviation: BP4mPy).Among the above-described compounds, the heterocyclic compounds havingquinoxaline skeletons or dibenzoquinoxaline skeletons, the heterocycliccompounds having diazine skeletons, and the heterocyclic compoundshaving pyridine skeletons have favorable reliability and can preferablybe used.

The following examples can also be given: metal complexes havingquinoline skeletons or benzoquinoline skeletons, such astris(8-quinolinolato)aluminum (abbreviation: Alq) andtris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃); andheteroaromatic compounds such as bathophenanthroline (abbreviation:BPhen), bathocuproine (abbreviation: BCP),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), and 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene(abbreviation: BzOs). In addition, high molecular compounds such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py) andpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can also be given.

Further, an electron-transport compound which easily accepts holes suchas 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:CzPA), 9-phenyl-3-[4-(10-phenyl-9-anthryflphenyl]-9H-carbazole(abbreviation: PCzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviatedto DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA), and2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA)can be preferably used. In the light-emitting element of one embodimentof the present invention, the electron-transport compound that dispersesthe blue-light-emitting hole-trapping fluorescent compound preferablyhas an anthracene skeleton to have a hole-trapping property in additionto an electron-transport property.

Examples of a hole-transport compound include a π-electron richheteroaromatic compound (e.g., a carbazole derivative or an indolederivative), an aromatic amine compound, and the like.

Specifically, the following examples can be given:4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)-triphenylamine(abbreviation: PCBNBB),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPA2SF),N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N-(9,9-dimethyl-2-N′,N′-diphenylamino-9H-fluoren-7-yl)-N′,N′-diphenylamine(abbreviation: DPNF),N,N′,N″-triphenyl-N,N′,N″-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),N,N′-bis[4-(carbazol-9-yl)phenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N′-phenyl-N′-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD), and3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthypamino]-9-phenylcarbazole(abbreviation: PCzTPN2).

The following examples can also be given: aromatic amine compounds suchas 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation:TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4,4′,4″-tris(N-carbazolyl)triphenylamine(abbreviation: TCTA), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), and4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi); and carbazole derivatives such as4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP), CzPA, and PCzPA. Inaddition, high molecular compounds such as poly(N-vinylcarbazole)(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD) can be given.

Here, for improvement in efficiency of energy transfer from a hostmaterial to a guest material, Förster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), whichare known as mechanisms of energy transfer between molecules, areconsidered. According to the mechanisms, it is preferable that anemission spectrum of a host material (fluorescence spectrum in energytransfer from a singlet excited state, phosphorescence spectrum inenergy transfer from a triplet excited state) largely overlap with anabsorption spectrum of a guest material (specifically, spectrum in anabsorption band on the longest wavelength (lowest energy) side).

However, in the case of a general phosphorescent guest material, it isdifficult to obtain an overlap between a fluorescence spectrum of a hostmaterial and an absorption spectrum in an absorption band on the longestwavelength (lowest energy) side of a guest material. The reason for thisis as follows: if the fluorescence spectrum of the host materialoverlaps with the absorption spectrum in the absorption band on thelongest wavelength (lowest energy) side of the guest material, since aphosphorescence spectrum of the host material is located on a longerwavelength (lower energy) side as compared to the fluorescence spectrum,the T₁ level of the host material becomes lower than the T₁ level of thephosphorescent compound and the above-described problem of quenchingoccurs; yet, when the host material is designed in such a manner thatthe T₁ level of the host material is higher than the T₁ level of thephosphorescent compound to avoid the problem of quenching, thefluorescence spectrum of the host material is shifted to the shorterwavelength (higher energy) side, and thus the fluorescence spectrum doesnot have any overlap with the absorption spectrum in the absorption bandon the longest wavelength (lowest energy) side of the guest material.For that reason, in general, it is difficult to obtain an overlapbetween a fluorescence spectrum of a host material and an absorptionspectrum in an absorption band on the longest wavelength (lowest energy)side of a guest material so as to maximize energy transfer from asinglet excited state of a host material.

Thus, it is preferable that in a light-emitting layer of alight-emitting element of one embodiment of the present invention, whichuses a phosphorescent compound as a guest material, a third substance becontained in addition to the phosphorescent compound and the hostmaterial (which are respectively regarded as a first substance and asecond substance contained in the light-emitting layer), and acombination of the host material the third substance form an exciplex(also referred to as excited complex). In that case, the host materialand the third substance form an exciplex at the time of recombination ofcarriers (electrons and holes) in the light-emitting layer. Thus, in thelight-emitting layer, fluorescence spectra of the host material and thethird substance are converted into an emission spectrum of the exciplexwhich is located on a longer wavelength side. Moreover, when the hostmaterial and the third substance are selected such that the emissionspectrum of the exciplex has a large overlap with the absorptionspectrum of the guest material, energy transfer from a singlet excitedstate can be maximized. Note that also in the case of a triplet excitedstate, energy transfer from the exciplex, not the host material, isassumed to occur. In one embodiment of the present invention to whichsuch a structure is applied, energy transfer efficiency can be improvedowing to energy transfer utilizing an overlap between an emissionspectrum of an exciplex and an absorption spectrum of a phosphorescentcompound; accordingly, a light-emitting element with high externalquantum efficiency can be provided.

Although any combination of the host material and the third substancecan be used as long as an exciplex is formed, an electron-trappingcompound (a compound that easily accepts electrons) and a hole-trappingcompound are preferably combined.

For example, as the host material and the third substance, theelectron-trap compound and the hole-trapping compound among theabove-described electron-transport compound or hole-transport compoundscan be used.

The materials which can be used as the host material or the thirdsubstance are not limited to the above materials as long as acombination of the material used as the host material and the materialused as the third substance can form an exciplex, an emission spectrumof the exciplex overlaps with an absorption spectrum of the guestmaterial, and a peak of the emission spectrum of the exciplex is locatedon a longer wavelength side than a peak of the absorption spectrum ofthe guest material.

Note that when an electron-trapping compound and a hole-trappingcompound are used for the host material and the third substance, carrierbalance can be controlled by the mixture ratio of the compounds.Specifically, the ratio of the host material to the third substance ispreferably from 1:9 to 9:1.

Further, the exciplex may be formed at the interface between two layers.For example, when a layer containing the electron-trapping compound anda layer containing the hole-trapping compound are stacked, the exciplexis formed in the vicinity of the interface thereof. These two layers maybe used as the light-emitting layer in the light-emitting element of oneembodiment of the present invention. These two layers may be used as thelight-emitting layer in one embodiment of the present invention. Thephosphorescent compound may be added to one of the two layers or both.

<Hole-Transport Layer>

The hole-transport layer 202 is a layer that contains a hole-transportsubstance.

The hole-transport substance is preferably a substance with a propertyof transporting more holes than electrons, and is especially preferablya substance with a hole mobility of 10⁻⁶ cm²/Vs or more.

For the hole-transport layer 202, it is possible to use any of thehole-transport compound that are described as examples of the substanceapplicable to the light-emitting layer.

Further, an aromatic hydrocarbon compound such as CzPA, t-BuDNA, DNA, orDPAnth can be used.

<Electron-Transport Layer>

The electron-transport layer 204 contains an electron-transportsubstance.

The electron-transport substance is preferably an organic compoundhaving a property of transporting more electrons than holes, and isespecially preferably a substance with an electron mobility of 10⁻⁶cm²/Vs or more.

For the electron-transport layer 204, it is possible to use any of theelectron-transport compounds that are described as examples of thesubstance applicable to the light-emitting layer.

<Hole-Injection Layer>

The hole-injection layer 201 is a layer containing a hole-injectionsubstance.

Examples of the hole-injection substance include metal oxides such asmolybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide,ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide,tantalum oxide, silver oxide, tungsten oxide, and manganese oxide.

A phthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc), or copper(II) phthalocyanine (abbreviation: CuPc) can also beused.

Further alternatively, it is possible to use an aromatic amine compoundwhich is a low molecular organic compound, such as TDATA, MTDATA, DPAB,DNTPD, 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), PCzPCA1, PCzPCA2, or PCzPCN1.

Further alternatively, it is possible to use a high molecular compoundsuch as PVK, PVTPA, PTPDMA, or Poly-TPD, or a high molecular compound towhich acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)or polyaniline/poly(styrenesulfonic acid) (PAni/PSS).

The hole-injection layer 201 may serve as the charge-generation region.When the hole-injection layer 201 in contact with the anode serves asthe charge-generation region, a variety of conductive materials can beused for the anode regardless of their work functions. Materialscontained in the charge-generation region will be described later.

<Electron-Injection Layer>

The electron-injection layer 205 contains an electron-injectionsubstance.

Examples of the electron-injection substance include an alkali metal, analkaline earth metal, a rare earth metal, and a compound thereof (e.g.,an oxide thereof, a carbonate thereof, and a halide thereof), such aslithium, cesium, calcium, lithium oxide, lithium carbonate, cesiumcarbonate, lithium fluoride, cesium fluoride, calcium fluoride, anderbium fluoride.

The electron-injection layer 205 may serve as the charge-generationregion. When the electron-injection layer 205 in contact with thecathode serves as the charge-generation region, any of a variety ofconductive materials can be used for the cathode regardless of theirwork functions. Materials contained in the charge-generation region willbe described later.

<Charge-Generation Region>

A charge-generation region included in a hole-injection layer or anelectron-injection layer and the charge-generation region 208 may haveeither a structure in which an electron acceptor (acceptor) is added toa hole-transport substance or a structure in which an electron donor(donor) is added to an electron-transport substance. Alternatively,these structures may be stacked.

The hole-transport compounds and the electron-transport compounds whichare described as examples of the substance that can be used for alight-emitting layer can be given as the hole-transport substance andthe electron-transport substance.

Further, as the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, atransition metal oxide can be given. In addition, an oxide of metalsthat belong to Group 4 to Group 8 of the periodic table can be given.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide are preferable since their electron-accepting property is high.Among these, molybdenum oxide is especially preferable since it isstable in the air and its hygroscopic property is low and is easilytreated.

Further, as the electron donor, it is possible to use an alkali metal,an alkaline earth metal, a rare earth metal, a metal belonging to Group13 of the periodic table, or an oxide or a carbonate thereof.Specifically, lithium, cesium, magnesium, calcium, ytterbium, indium,lithium oxide, cesium carbonate, or the like is preferably used.Alternatively, an organic compound such as tetrathianaphthacene may beused as the electron donor.

<Electron-Injection Buffer Layer>

The electron-injection buffer layer 206 contains an electron-injectionsubstance. The electron-injection buffer layer 206 is a layer thatfacilitates electron injection from the charge generation region 208into the EL layer 103. As the high electron-injection substance, any ofthe above-described substances can be used. Alternatively, theelectron-injection buffer layer 206 may contain any of theabove-described electron-transport substances and donor substances.

<Electron-Relay Layer>

The electron-relay layer 207 immediately accepts electrons drawn out ofthe acceptor substance in the charge-generation region 208.

The electron-relay layer 207 contains an electron-transport substance.As the electron-transport substance, a phthalocyanine-based material ora metal complex having a metal-oxygen bond and an aromatic ligand ispreferably used.

As the phthalocyanine-based substance, specifically, it is possible touse CuPc, a phthalocyanine tin(II) complex (SnPc), a phthalocyanine zinccomplex (ZnPc), cobalt(II) phthalocyanine, b-form (CoPc), phthalocyanineiron (FePc), or vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine(PhO-VOPc).

As the metal complex having a metal-oxygen bond and an aromatic ligand,a metal complex having a metal-oxygen double bond is preferably used. Ametal-oxygen double bond has an acceptor property; thus, electrons cantransfer (be donated and accepted) more easily.

As the metal complex having a metal-oxygen bond and an aromatic ligand,a phthalocyanine-based material is also preferably used. In particular,vanadyl phthalocyanine (VOPc), a phthalocyanine tin(IV) oxide complex(SnOPc), or a phthalocyanine titanium oxide complex (TiOPc) ispreferable because a metal-oxygen double bond is more likely to act onanother molecule in terms of a molecular structure and an acceptorproperty is high.

As the phthalocyanine-based material, a phthalocyanine-based materialhaving a phenoxy group is preferably used. Specifically, aphthalocyanine derivative having a phenoxy group, such as PhO-VOPc, ispreferably used. The phthalocyanine derivative having a phenoxy group issoluble in a solvent; thus, the phthalocyanine derivative has anadvantage of being easily handled during formation of a light-emittingelement and an advantage of facilitating maintenance of an apparatusused for film formation.

Examples of other electron-transport substances include perylenederivatives such as 3,4,9,10-perylenetetracarboxylic dianhydride(abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxylic bisbenzimidazole(abbreviation: PTCBI), N,N′-dioctyl-3,4,9,10-perylenetetracarboxylicdiimide (abbreviation: PTCDI-C8H),N,N′-dihexyl-3,4,9,10-perylenetetracarboxylic diimide (abbreviation: HexPTC), and the like. Alternatively, it is possible to use anitrogen-containing condensed aromatic compound such aspirazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (abbreviation:PPDN), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene(abbreviation: HAT(CN)₆), 2,3-diphenylpyrido[2,3-b]pyrazine(abbreviation: 2PYPR), or 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine(abbreviation: F2PYPR). The nitrogen-containing condensed aromaticcompound is preferably used for the electron-relay layer 207 because ofits stability.

Further alternatively, it is possible to use7,7,8,8-tetracyanoquinodimethane (abbreviation: TCNQ),1,4,5,8-naphthalenetetracarboxylicdianhydride (abbreviation: NTCDA),perfluoropentacene, copper hexadecafluoro phthalocyanine (abbreviation:F₁₆CuPc),N,N′-bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)-1,4,5,8-naphthalenetetracarboxylic diimide (abbreviation: NTCDI-C8F),3′,4′-dibutyl-5,5″-bis(dicyanomethylene)-5,5″-dihydro-2,2′:5′,2″-terthiophene(abbreviation: DCMT), or a methanofullerene (e.g., [6,6]-phenyl C₆₁butyric acid methyl ester).

The electron-relay layer 207 may further contain any of theabove-described donor materials. When the donor material is contained inthe electron-relay layer 207, electrons can transfer easily and thelight-emitting element can be driven at a lower voltage.

The LUMO levels of the substance with a high electron-transport propertyand the donor substance are preferably −5.0 eV to −3.0 eV, i.e., betweenthe LUMO level of the acceptor substance contained in thecharge-generation region 208 and the LUMO level of the substance with ahigh electron-transport property contained in the electron-transportlayer 204 (or the LUMO level of the EL layer 103 in contact with theelectron-relay layer 207 or with the electron-injection buffer layer206). When a donor substance is contained in the electron-relay layer207, as the electron-transport substance, a substance with a LUMO levelhigher than the acceptor level of the acceptor substance contained inthe charge-generation region 208 can be used.

The above-described layers included in the EL layer 103 and theintermediate layer 107 can be formed separately by any of the followingmethods: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, a coatingmethod, and the like.

With the use of a light-emitting element described in this embodiment, apassive matrix light-emitting device or an active matrix light-emittingdevice in which driving of the light-emitting element is controlled by atransistor can be manufactured. Furthermore, the light-emitting devicecan be applied to an electronic device, a lighting device, or the like.

This embodiment can be freely combined with other embodiments.

(Embodiment 2)

In this embodiment, a light-emitting device of one embodiment of thepresent invention will be described with reference to FIG. 2 and FIGS.3A and 3B. FIGS. 3A and 3B are cross-sectional views taken along chainline M-N in FIG. 2.

The light-emitting device including a light-emitting element of oneembodiment of the present invention has high emission efficiency. Inaddition, the light-emitting element one embodiment of the presentinvention can be favorably used in a flexible light-emitting device.

The light-emitting device in FIG. 3A includes a top-emissionlight-emitting element 350 over a supporting substrate 300 with aninsulating film 304 provided therebetween. The light-emitting element350 includes a first electrode 301, an EL layer 302, and a secondelectrode 303. The second electrode 303 has a transmitting property withrespect to visible light. An end portion of the first electrode 301 andan end portion of a terminal 310 are covered with a partition wall 305.An auxiliary wiring 306 is provided over the first electrode 301 withthe partition wall 305 provided therebetween. The auxiliary wiring 306is electrically connected to the second electrode 303. The supportingsubstrate 300 and a sealing substrate 308 are attached to each otherwith a sealing material 307. A light extraction structure 309 isprovided over a surface of the sealing substrate 308.

The light-emitting device in FIG. 3B includes a top-emissionlight-emitting element 360 over the supporting substrate 300 with theinsulating film 304 provided therebetween. The light-emitting element360 includes a first electrode 321, an EL layer 322, and a secondelectrode 323. The first electrode 321 has a transmitting property withrespect to visible light. An end portion of the first electrode 321 andthe end portion of the terminal 310 are covered with the partition wall305. The auxiliary wiring 306 is provided over the first electrode 321.The partition wall 305 is provided to cover the auxiliary wiring 306.The auxiliary wiring 306 is electrically connected to the firstelectrode 321. The supporting substrate 300 and the sealing substrate308 are attached to each other with the sealing material 307. The lightextraction structure 309 is provided over a surface of the supportingsubstrate 300.

Examples of materials that can be used for the light-emitting device ofone embodiment of the present invention will be described.

[Substrate]

The substrate on the side from which light from the light-emittingelement is extracted is formed using a material which transmits thelight. For example, a material such as glass, quartz, ceramics,sapphire, or an organic resin can be used. The substrate of a flexiblelight-emitting device is formed using a flexible material.

As the glass, for example, non-alkali glass, barium borosilicate glass,aluminoborosilicate glass, or the like can be used.

Examples of a material having flexibility and a light-transmittingproperty with respect to visible light include flexible glass, polyesterresins such as polyethylene terephthalate (PET) and polyethylenenaphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, apolystyrene resin, a polyamide imide resin, and a polyvinyl chlorideresin. In particular, a material whose thermal expansion coefficient islow is preferred, and for example, a polyamide imide resin, a polyimideresin, or PET can be suitably used. A substrate in which a glass fiberis impregnated with an organic resin or a substrate whose thermalexpansion coefficient is reduced by mixing an organic resin with aninorganic filler can also be used. A substrate using such a material islightweight, and thus a light-emitting device using this substrate canalso be lightweight.

Furthermore, since the substrate through which light emission is notextracted does not need to have a light-transmitting property, a metalsubstrate using a metal material or an alloy material or the like can beused in addition to the above-mentioned substrates. A metal material andan alloy material, which have high thermal conductance, are preferred inthat they can easily conduct heat into the whole sealing substrate andaccordingly can reduce a local rise in the temperature of thelight-emitting device. To obtain flexibility and bendability, thethickness of a metal substrate is preferably greater than or equal to 10μm and less than or equal to 200 μm, more preferably greater than orequal to 20 μm and less than or equal to 50 μm.

There is no particular limitation on a material of the metal substrate,but it is preferable to use, for example, aluminum, copper, nickel, ametal alloy such as an aluminum alloy or stainless steel.

It is preferable to use a substrate subjected to insulation treatment insuch a manner that a surface of the conductive substrate is oxidized oran insulating film is formed on the surface. An insulating film may beformed by, for example, a coating method such as a spin-coating methodand a dipping method, an electrodeposition method, an evaporationmethod, or a sputtering method. An oxide film may be formed over thesubstrate surface by a known method such as an anodic oxidation method,exposing to or heating in an oxygen atmosphere, or the like.

The flexible substrate may have a stacked structure in which a hard coatlayer (such as a silicon nitride layer) by which a surface of alight-emitting device is protected from damage, a layer (such as anaramid resin layer) which can disperse pressure, or the like is stackedover a layer of any of the above-mentioned materials. Furthermore, tosuppress a decrease in the lifetime of the light-emitting element due tomoisture and the like, an insulating film with low water permeabilitymay be provided. For example, a film containing nitrogen and silicon(e.g., a silicon nitride film, a silicon oxynitride film), or a filmcontaining nitrogen and aluminum (e.g., an aluminum nitride film) may beprovided.

The substrate may be formed by stacking a plurality of layers. When aglass layer is used, a barrier property against water and oxygen can beimproved and thus a reliable light-emitting device can be provided.

A substrate in which a glass layer, a bonding layer, and an organicresin layer are stacked from the side closer to a light-emitting elementis preferably used. The thickness of the glass layer is greater than orequal to 20 μm and less than or equal to 200 μm, preferably greater thanor equal to 25 μm and less than or equal to 100 μm. With such athickness, the glass layer can have both a high barrier property againstwater and oxygen and a high flexibility. The thickness of the organicresin layer is greater than or equal to 10 μm and less than or equal to200 μm, preferably greater than or equal to 20 μm and less than or equalto 50 μm. By providing such an organic resin layer on an outer side thanthe glass layer, occurrence of a crack or a break in the glass layer canbe suppressed and mechanical strength can be improved. With thesubstrate that includes such a composite material of a glass materialand an organic resin, a highly reliable and flexible light-emittingdevice can be provided.

[Insulating Film]

An insulating film may be provided between the supporting substrate andthe light-emitting element. The insulating film can be formed using aninorganic insulating material such as silicon oxide, silicon nitride,silicon oxynitride, or silicon nitride oxide. In order to suppress theentrance of moisture or the like into the light-emitting element, aninsulating film with low water permeability such as a silicon oxidefilm, a silicon nitride film, or an aluminum oxide film is particularlypreferable. For a similar purpose and with a similar material, aninsulating film covering the light-emitting element may be provided.

[Light-Emitting Element]

The light emitting device of one embodiment of the present inventionincludes at least one the light emitting elements described inEmbodiment 1.

[Partition Wall]

For the partition wall, an organic resin or an inorganic insulatingmaterial can be used. As the organic resin, for example, a polyimideresin, a polyamide resin, an acrylic resin, a siloxane resin, an epoxyresin, a phenol resin, or the like can be used. As the inorganicinsulating material, silicon oxide, silicon oxynitride, or the like canbe used. In particular, a photosensitive resin is preferably used foreasy formation of the partition wall.

There is no particular limitation on the method for forming thepartition wall. A photolithography method, a sputtering method, anevaporation method, a droplet discharging method (e.g., an inkjetmethod), a printing method (e.g., a screen printing method or an offsetprinting method), or the like can be used.

[Auxiliary Wiring]

An auxiliary wiring is not necessarily provided; however, an auxiliarywiring is preferably provided because voltage drop due to the resistanceof an electrode can be prevented.

For a material of the auxiliary wiring, a single layer or a stackedlayer using a material selected from copper (Cu), titanium (Ti),tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium(Nd), scandium (Sc), or nickel (Ni) or an alloy material including anyof these materials as its main component is used. In that case, in orderto prevent the above problem of corrosion, a stacked layer is formed andaluminum is used for a layer which is not in contact with ITO or thelike. The thickness of the auxiliary wiring can be greater than or equalto 0.1 μm and less than or equal to 3 μm, preferably greater than orequal to 0.1 μm and less than or equal to 0.5 μm.

Metal paste (e.g., silver paste) may be used for the material of theauxiliary wiring. In this case, the auxiliary wiring can be formed ofgathered particles of the metal. Therefore, the surface of the auxiliarywiring is rough and it is difficult for the EL layer to completely coverthe auxiliary wiring; accordingly, the upper electrode and the auxiliarywiring are easily connected electrically to each other.

[Sealing Material]

A method for sealing the light-emitting device is not limited, andeither solid sealing or hollow sealing can be employed. For example, aglass material such as a glass frit, or a resin material such as atwo-component-mixture-type resin which is curable at room temperature, alight curable resin, a thermosetting resin, and the like can be used.The light-emitting device may be filled with an inert gas such asnitrogen or argon, or resin such as a polyvinyl chloride (PVC) resin, anacrylic resin, a polyimide resin, an epoxy resin, a silicone resin, apolyvinyl butyral (PVB) resin, or an ethylene vinyl acetate (EVA) resin.Further, a drying agent may be contained in the resin.

[Light Extraction Structure]

For the light extraction structure, a hemispherical lens, a micro lensarray, a film provided with an uneven surface structure, a lightdiffusing film, or the like can be used. For example, a light extractionstructure 309 can be formed by attaching the lens or film to thesubstrate with an adhesive or the like which has substantially the samerefractive index as the substrate or the lens or film.

[Transistor]

The light-emitting device of one embodiment of the present invention mayinclude a transistor. The structure of the transistor is not limited: atop-gate transistor may be used, or a bottom-gate transistor such as aninverted staggered transistor may be used. An n-channel transistor maybe used and a p-channel transistor may also be used. In addition, thereis no particular limitation on a material used for the transistor. Forexample, a transistor in which silicon or an oxide semiconductor such asan In—Ga—Zn-based metal oxide is used in a channel formation region canbe employed.

This embodiment can be freely combined with other embodiments.

(Embodiment 3)

In this embodiment, an example of a method for manufacturing alight-emitting device, according to one embodiment of the presentinvention will be described with reference to FIGS. 4A to 4E and FIGS.5A to 5E. The light-emitting device of this embodiment is a flexiblelight-emitting device manufactured by a technique in which some elementsof the light-emitting device are formed over a formation substrate, andthen the elements are transferred from the formation substrate to aflexible substrate.

When a material which is flexible but has high water permeability andlow heat resistance (e.g., resin) has to be used for a substrate of aflexible light-emitting device, the substrate can not be exposed to hightemperature in the manufacturing process. Thus, conditions formanufacturing a transistor and an insulating film over the substrate arelimited. In the manufacturing method of this embodiment, a transistorand the like can be fowled over a formation substrate having high heatresistance; thus, a highly reliable transistor and an insulating filmwhose water permeability is sufficiently reduced can be formed. Then,these are transferred to a flexible substrate and thus a highly reliableflexible light-emitting device can be manufactured.

<Method A for Manufacturing Light-Emitting Device>

First, a separation layer 603 is formed over a formation substrate 601,and a layer 605 to be separated (hereinafter referred to as layer 605)is formed over the separation layer 603 (FIG. 4A).

There is no particular limitation on a layer formed as the layer 605.For example, an insulating film with low water permeability, atransistor, a light-emitting element, a color filter, and the like aregiven. For example, an insulating film with low water permeability, atransistor, an insulating film covering the transistor, a planarizationfilm, a lower electrode of the light-emitting element, and a partitionwall covering an end portion of the lower electrode can be formed as thelayer 605. Further, an EL layer and an upper electrode of thelight-emitting element, a sealing film covering the light-emittingelement and the like may be provided in the layer 605. Alternatively,only an insulating film with low water permeability may be formed as thelayer 605, and a transistor and the like may be formed after theseparation and transfer process.

A glass substrate, a quartz substrate, a sapphire substrate, a ceramicsubstrate, a metal substrate, or the like can be used as the formationsubstrate 601.

For the glass substrate, for example, a glass material such asaluminosilicate glass, aluminoborosilicate glass, or barium borosilicateglass can be used. When the temperature of the heat treatment performedlater is high, a substrate having a strain point of 730° C. or higher ispreferably used. Note that by containing a large amount of barium oxide(BaO), a glass substrate which is heat-resistant and more practical canbe obtained. Alternatively, crystallized glass or the like may be used.

In the case where a glass substrate is used as the formation substrate601, an insulating film such as a silicon oxide film, a siliconoxynitride film, a silicon nitride film, or a silicon nitride oxide filmis preferably formed between the formation substrate 601 and theseparation layer 603, in which case contamination from the glasssubstrate can be prevented.

The separation layer 603 has a single-layer structure or a layeredstructure containing an element selected from tungsten, molybdenum,titanium, tantalum, niobium, nickel, cobalt, zirconium, zinc, ruthenium,rhodium, palladium, osmium, iridium, and silicon; an alloy materialcontaining any of the elements; or a compound material containing any ofthe elements. A crystal structure of a layer containing silicon may beamorphous, microcrystal, or polycrystal.

The separation layer 603 can be formed by a sputtering method, a plasmaCVD method, a coating method, a printing method, or the like. Note thata coating method includes a spin coating method, a droplet dischargemethod, and a dispensing method.

In the case where the separation layer 603 has a single-layer structure,a tungsten layer, a molybdenum layer, or a layer containing a mixture oftungsten and molybdenum is preferably formed. Alternatively, a layercontaining an oxide or an oxynitride of tungsten, a layer containing anoxide or an oxynitride of molybdenum, or a layer containing an oxide oran oxynitride of a mixture of tungsten and molybdenum may be formed.Note that the mixture of tungsten and molybdenum corresponds to an alloyof tungsten and molybdenum, for example.

In the case where the separation layer 603 has a layered-structureincluding a layer containing tungsten and a layer containing an oxide oftungsten, the layer containing an oxide of tungsten may be formed asfollows: the layer containing tungsten is formed first and an insulatingfilm formed of an oxide is formed thereover, so that the layercontaining an oxide of tungsten is formed at the interface between thetungsten layer and the insulating film. Alternatively, the layercontaining an oxide of tungsten may be formed by performing thermaloxidation treatment, oxygen plasma treatment, treatment with a highlyoxidizing solution such as ozone water, or the like on the surface ofthe layer containing tungsten. Plasma treatment or heat treatment may beperformed in an atmosphere of oxygen, nitrogen, nitrous oxide alone, ora mixed gas of any of these gasses and another gas. Surface condition ofthe separation layer 603 is changed by the plasma treatment or heattreatment, whereby adhesion between the separation layer 603 and theinsulating film formed later can be controlled.

The insulating film included in the layer 605 preferably has asingle-layer structure or a layered structure including any of a siliconnitride film, a silicon oxynitride film, a silicon nitride oxide film,and the like.

The insulating film can be formed by a sputtering method, a plasma CVDmethod, a coating method, a printing method, or the like. For example,the insulating film is formed at a temperature of higher than or equalto 250° C. and lower than or equal to 400° C. by a plasma CVD method,whereby a dense film having very low water permeability can be obtained.Note that the insulating film is preferably formed to have a thicknessof greater than or equal to 10 nm and less than or equal to 3000 nm,further preferably greater than or equal to 200 nm and less than orequal to 1500 nm.

Next, the layer 605 and a temporary supporting substrate 607 are bondedwith a separation adhesive 609, and the layer 605 is separated from theformation substrate 601 along the separation layer 603. By this process,the layer 605 to be separated is placed on the temporary supportingsubstrate 607 side (FIG. 4B).

As the temporary supporting substrate 607, a glass substrate, a quartzsubstrate, a sapphire substrate, a ceramic substrate, a metal substrate,or the like can be used. Alternatively, a plastic substrate that canwithstand a processing temperature in this embodiment may be used, or aflexible film-like substrate may be used.

An adhesive with which the temporary supporting substrate 607 and thelayer 605 can be chemically or physically separated when necessary, suchas an adhesive that is soluble in water or a solvent or an adhesivewhich is capable of being plasticized upon irradiation of UV light orthe like, is used as the separation adhesive 609.

Any of various methods can be used as appropriate as the process fortransferring the layer to the temporary supporting substrate. Forexample, when a layer including a metal oxide film is formed as theseparation layer on the side in contact with the layer to be separated,the metal oxide film is embrittled by crystallization, whereby the layerto be separated can be separated from the formation substrate.Alternatively, when an amorphous silicon film containing hydrogen isformed as the separation layer between a formation substrate having highheat resistance and a layer to be separated, the amorphous silicon filmis removed by laser light irradiation or etching, whereby the layer tobe separated can be separated from the formation substrate.Alternatively, after a layer including a metal oxide film is formed asthe separation layer on the side in contact with the layer to beseparated, the metal oxide film is embrittled by crystallization, andpart of the separation layer is removed by etching using a solution or afluoride gas such as NF₃, BrF₃, or ClF₃, whereby the separation can beperformed at the embrittled metal oxide film. Furthermore, a method maybe used in which a film containing nitrogen, oxygen, hydrogen, or thelike (for example, an amorphous silicon film containing hydrogen, analloy film containing hydrogen, an alloy film containing oxygen, or thelike) is used as the separation layer, and the separation layer isirradiated with laser light to release the nitrogen, oxygen, or hydrogencontained in the separation layer as a gas, thereby promoting separationbetween the layer to be separated and the formation substrate.Alternatively, it is possible to use a method in which the formationsubstrate provided with the layer to be separated is removedmechanically or by etching using a solution or a fluoride gas such asNF₃, BrF₃, or ClF₃, or the like. In this case, the separation layer isnot necessarily provided.

Further, the transfer process can be conducted easily by combination ofthe above-described separation methods. In other words, separation canbe performed with physical force (by a machine or the like) afterperforming laser light irradiation, etching on the separation layer witha gas, a solution, or the like, or mechanical removal with a sharpknife, scalpel or the like so that the separation layer and the layer tobe separated can be easily separated from each other.

Alternatively, the layer may be separated from the formation substrateafter an interface between the separation layer and the layer isintroduced to a liquid. The separation may be performed while pouring aliquid such as water.

As another separation method, the separation layer 603 formed usingtungsten may be separated while etching the separation layer 603 using amixed solution of ammonium water and a hydrogen peroxide solution.

Next, with an adhesive layer 653 including an adhesive different fromthe separation adhesive 609, a first flexible substrate 651 is bonded tothe separation layer 603 or the layer 605 which is exposed by theseparation from the formation substrate 601 (FIG. 4C).

After that, the temporary supporting substrate 607 is removed bydissolving or plasticizing the separation adhesive 609. After thetemporary supporting substrate 607 is removed, the separation adhesive609 is removed using water, a solvent, or the like to expose the layer605 (FIG. 4D).

Through the above steps, the layer 605 can be formed over the firstflexible substrate 651.

After that, other elements of the light-emitting device are formed, andthen a second flexible substrate 659 is bonded thereto with an adhesivelayer 657 (FIG. 4E).

In the above-described manner, the light-emitting device of oneembodiment of the present invention can be manufactured.

Note that the separation layer is not necessary in the case where theformation substrate and the layer to be separated can be separated attheir interface. For example, glass is used as the formation substrate601, an organic resin such as polyimide is formed in contact with theglass, and the insulating film, the transistor, and the like are formedover the organic resin. In this case, heating the organic resin enablesthe separation at the interface between the formation substrate 601 andthe organic resin. Then, the organic resin and the first flexiblesubstrate 651 can be bonded with the adhesive layer 653. Alternatively,separation at the interface between a metal layer and the organic resinmay be performed in the following manner: the metal layer is providedbetween the formation substrate and the organic resin and current ismade to flow in the metal layer so that the metal layer is heated.

<Method B for Manufacturing Light-Emitting Device>

First, a separation layer 603 is formed over a formation substrate 601,and a layer 605 to be separated (hereinafter referred to as layer 605)is formed over the separation layer 603 (FIG. 5A).

A separation layer 663 is formed over a formation substrate 661, and alayer 665 to be separated (hereinafter referred to as layer 665) isformed over the separation layer 663 (FIG. 5B).

Next, the formation substrate 601 and the formation substrate 661 arebonded with the adhesive layer 657 (FIG. 5C).

Then, the layer 605 is separated from the formation substrate 601 alongthe separation layer 603. Then, the first flexible substrate 651 isbonded to the separation layer 603 or the layer 605 which is exposed byseparation from the formation substrate 601, with the adhesive layer 653(FIG. 5D).

Similarly, the layer 665 is separated from the formation substrate 661along the separation layer 663. Then, the second flexible substrate 659is bonded to the separation layer 663 or the layer 665 which is exposedby separation from the formation substrate 651, with the adhesive layer668 (FIG. 5E).

In the above-described manner, the light-emitting device of oneembodiment of the present invention can be manufactured.

In the method for manufacturing a light-emitting device described inthis embodiment, any of curable adhesives can be used as the adhesivelayers 653, 657, and 668; for example, a light curable adhesive such asa UV curable adhesive, a reactive curable adhesive, a thermosettingadhesive, and an anaerobic adhesive can be used. The examples include anepoxy resin, an acrylic resin, a silicone resin, a phenol resin, and thelike. In particular, a material with low moisture permeability, such asan epoxy resin, is preferred. Further, the above adhesives may include adrying agent (such as zeolite). Accordingly, deterioration of thelight-emitting element can be suppressed. A curable adhesive provided onthe side through which light emitted from the light-emitting element isextracted is a light-transmitting material, preferably with a highrefractive index. For example, by mixing a filler with a high refractiveindex (e.g., titanium oxide or zirconium) into the adhesive layer, lightfrom the light-emitting element can be extracted efficiently.

This embodiment can be freely combined with other embodiments.

(Embodiment 4)

In this embodiment, a light-emitting device which is one embodiment ofthe present invention is described with reference to FIGS. 6A and 6B andFIGS. 7A and 7B. The light-emitting device of this embodiment includes alight-emitting element of one embodiment of the present invention. Thelight-emitting element has high emission efficiency and thus alight-emitting device with low power consumption can be obtained.

FIG. 6A is a plan view of a light-emitting device of one embodiment ofthe present invention, and FIG. 6B is a cross-sectional view taken alonga dashed-dotted line A-B in FIG. 6A.

In the light-emitting device of this embodiment, a light-emittingelement 403 is included in a space 415 surrounded by a supportingsubstrate 401, a sealing substrate 405, and a sealing material 407. Thelight-emitting element 403 is a light-emitting element having abottom-emission structure; specifically, the first electrode 421 whichtransmits visible light is provided over the supporting substrate 401,the EL layer 423 is provided over the first electrode 421, and thesecond electrode 425 which reflects visible light is provided over theEL layer 423. The light-emitting element 403 is a light-emitting elementof one embodiment of the present invention in Embodiment 1. The sealingsubstrate 405 includes a drying agent 418 on the light-emitting element403 side.

A first terminal 409 a is electrically connected to an auxiliary wiring417 and the first electrode 421. An insulating layer 419 is provided ina region which overlaps with the auxiliary wiring 417 over the firstelectrode 421. The first terminal 409 a and the second electrode 425 areelectrically insulated by the insulating layer 419. The second terminal409 b is electrically connected to the second electrode 425. Note thatalthough the first electrode 421 is formed over the auxiliary wiring 417in this embodiment, the auxiliary wiring 417 may be formed over thefirst electrode 421.

Therefore, a light extraction structure 411 a is preferably provided atthe interface between the supporting substrate 401 and the atmosphere.Therefore when provided at the interface between the supportingsubstrate 401 and the atmosphere, the light extraction structure 411 acan reduce light which cannot be extracted to the atmosphere due tototal reflection, resulting in an increase in the light extractionefficiency of the light-emitting device.

A light extraction structure 411 b is preferably provided at aninterface between the light-emitting element 403 and the supportingsubstrate 401. In the case where the light extraction structure 411 bhas unevenness, a planarization layer 413 is preferably provided betweenthe light extraction structure 411 b and the first electrode 421. Thus,the first electrode 421 can be a flat film, and occurrence of leakagecurrent in the EL layer 423 due to the unevenness of the first electrode421 can be suppressed. Moreover, since the light extraction structure411 b is provided at an interface between the planarization layer 413and the supporting substrate 401, light which cannot be extracted to theatmosphere due to total reflection can be reduced, so that the lightextraction efficiency of the light-emitting device can be improved.

The planarization layer 413 is more flat in its one surface that is incontact with the first electrode 421 than in its other surface that isin contact with the light extraction structure 411 b. As a material ofthe planarization layer 413, glass, liquid, a resin, or the like havinga light-transmitting property and a high refractive index can be used.

FIG. 7A is a plan view of a light-emitting device of one embodiment ofthe present invention. FIG. 7B is a cross-sectional view taken alongdashed-dotted line C-D in FIG. 7A.

An active matrix light-emitting device according to this embodimentincludes, over a supporting substrate 501, a light-emitting portion 551,a driver circuit portion 552 (gate side driver circuit portion), adriver circuit portion 553 (source side drive circuit portion), and thesealant 507. The light-emitting portion 551, the driver circuit portions552 and 553 are formed in a space 515 formed by the supporting substrate501, a sealing substrate 505, and the sealant 507.

Any of a separate coloring method, a color filter method, and a colorconversion method can be applied to the light-emitting device of oneembodiment of the present invention. The light-emitting portion 551formed by a separate coloring method is illustrated in FIG. 7B.

The light-emitting portion 551 includes a plurality of light-emittingunits each including a switching transistor 541 a, a current controltransistor 541 b, and a second electrode 525 electrically connected to awiring (a source electrode or a drain electrode) of the transistor 541b.

A light-emitting element 503 included in the light-emitting portion 551has a bottom-emission structure and includes a first electrode 521 whichtransmits visible light, an EL layer 523, and the second electrode 525.Further, a partition wall 519 is formed so as to cover an end portion ofthe first electrode 521. In the EL layer 523, at least layers (e.g.,light-emitting layers) which contain a variable material depending onthe light-emitting element are colored separately.

Over the supporting substrate 501, a lead wiring 517 for connecting anexternal input terminal through which a signal (e.g., a video signal, aclock signal, a start signal, or a reset signal) or a potential from theoutside is transmitted to the driver circuit portions 552 and 553 isprovided. Here, an example in which a flexible printed circuit (FPC) 509is provided as the external input terminal is described.

The driver circuit portions 552 and 553 have a plurality of transistors.FIG. 7B illustrates two of the transistors in the driver circuit portion552 (transistors 542 and 543).

To prevent an increase in the number of manufacturing steps, the leadwiring 517 is preferably formed using the same material and the samestep(s) as those of the electrode or the wiring in the light-emittingportion or the driver circuit portion. Described in this embodiment isan example in which the lead wiring 517 is formed using the samematerial and the same step(s) as those of the source electrode and thedrain electrode of the transistor included in the light-emitting portion551 and the driver circuit portion 552.

In FIG. 7B, the sealing material 507 is in contact with a firstinsulating layer 511 over the lead wiring 517. The adhesion of thesealing material 507 to metal is low in some cases. Therefore, thesealing material 507 is preferably in contact with an inorganicinsulating film over the lead wiring 517. Such a structure enables alight-emitting device to have high sealing capability, high adhesion,and high reliability. As examples of the inorganic insulating film, anoxide film of a metal or a semiconductor, a nitride film of a metal or asemiconductor, and a oxynitride film of a metal or a semiconductor aregiven; specifically, a silicon oxide film, a silicon nitride film, asilicon oxynitride film, a silicon nitride oxide film, an aluminum oxidefilm, a titanium oxide film, and the like can be given.

The first insulating layer 511 has an effect of preventing diffusion ofimpurities into a semiconductor included in the transistor. As thesecond insulating layer 513, an insulating film with a planarizationfunction is preferably selected in order to reduce surface unevennessdue to the transistor.

This embodiment can be combined with any of other embodiments, asappropriate.

(Embodiment 5)

In this embodiment, examples of electronic devices and lighting devicesto which the light-emitting device of one embodiment of the presentinvention is applied will be described with reference to FIGS. 8A to 8Eand FIGS. 9A and 9B.

Electronic devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a display portion.Lighting devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a light-emittingportion (lighting portion). An electronic device and a lighting devicewith low power consumption can be provided by adopting thelight-emitting device of one embodiment of the present invention.

Examples of the electronic devices to which the light-emitting device isapplied are television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, cameras such as digitalcameras and digital video cameras, digital photo frames, cellular phones(also referred to as portable telephone devices), portable gamemachines, portable information terminals, audio playback devices, largegame machines such as pin-ball machines, and the like. Specific examplesof these electronic devices and lighting devices are illustrated inFIGS. 8A to 8E and FIGS. 9A and 9B.

FIG. 8A illustrates an example of a television set. In a televisiondevice 7100, a display portion 7102 is incorporated in a housing 7101.The display portion 7102 is capable of displaying images. Thelight-emitting device to which one embodiment of the present inventionis applied can be used for the display portion 7102. In addition, here,the housing 7101 is supported by a stand 7103.

The television device 7100 can be operated with an operation switchprovided in the housing 7101 or a separate remote controller 7111. Withoperation keys of the remote controller 7111, channels and volume can becontrolled and images displayed on the display portion 7102 can becontrolled. Further, the remote controller 7111 may be provided with adisplay portion for displaying data output from the remote controller7111.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the receiver, a general television broadcastcan be received. Furthermore, when the television device 7100 isconnected to a communication network by wired or wireless connection viathe modem, one-way (from a transmitter to a receiver) or two-way(between a transmitter and a receiver, between receivers, or the like)data communication can be performed.

FIG. 8B illustrates an example of a computer. A computer 7200 includes amain body 7201, a housing 7202, a display portion 7203, a keyboard 7204,an external connecting port 7205, a pointing device 7206, and the like.Note that this computer is manufactured by using the light-emittingdevice of one embodiment of the present invention for the displayportion 7203.

FIG. 8C illustrates an example of a portable game machine. A portablegame machine 7300 has two housings, a housing 7301 a and a housing 7301b, which are connected with a joint portion 7302 so that the portablegame machine can be opened or closed. A display portion 7303 a isincorporated in the housing 7301 a and a display portion 7303 b isincorporated in the housing 7301 b. In addition, the portable gamemachine illustrated in FIG. 8C includes a speaker portion 7304, arecording medium insertion portion 7305, an operation key 7306, aconnection terminal 7307, a sensor 7308 (a sensor having a function ofmeasuring or sensing force, displacement, position, speed, acceleration,angular velocity, rotational frequency, distance, light, liquid,magnetism, temperature, chemical substance, sound, time, hardness,electric field, electric current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), anLED lamp, a microphone, and the like. The structure of the portable gamemachine is not limited to the above as long as the light-emitting deviceaccording to one embodiment of the present invention is used for atleast either the display portion 7303 a or the display portion 7303 b,or both of them. The portable game machine may be provided with otheraccessories as appropriate. The portable game machine illustrated inFIG. 8C has a function of reading a program or data stored in arecording medium to display it on the display portion, and a function ofsharing data with another portable game machine by wirelesscommunication. Note that a function of the portable game machineillustrated in FIG. 8C is not limited to the above, and the portablegame machine can have a variety of functions.

FIG. 8D illustrates an example of a cellular phone. A cellular phone7400 is provided with a display portion 7402 incorporated in a housing7401, operation buttons 7403, an external connection port 7404, aspeaker 7405, a microphone 7406, and the like. Note that the mobilephone 7400 is manufactured by using the light-emitting device of oneembodiment of the present invention for the display portion 7402.

When the display portion 7402 of the mobile phone 7400 illustrated inFIG. 8D is touched with a finger or the like, data can be input into themobile phone 7400. Further, operations such as making a call andcreating e-mail can be performed by touch on the display portion 7402with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting data such as text. The thirdmode is a display-and-input mode in which two modes of the display modeand the input mode are combined.

For example, in the case of making a call or composing an e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on a screen can be inputted.

When a detection device including a sensor for detecting inclination,such as a gyroscope sensor or an acceleration sensor, is provided insidethe mobile phone 7400, display on the screen of the display portion 7402can be automatically changed by determining the orientation of themobile phone 7400 (whether the mobile phone is placed horizontally orvertically for a landscape mode or a portrait mode).

The screen modes are switched by touching the display portion 7402 oroperating the operation buttons 7403 of the housing 7401. Alternatively,the screen modes can be switched depending on kinds of images displayedon the display portion 7402. For example, when a signal of an imagedisplayed on the display portion is a signal of moving image data, thescreen mode is switched to the display mode. When the signal is a signalof text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed within a specified period while a signal detectedby an optical sensor in the display portion 7402 is detected, the screenmode may be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits a near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

FIG. 8E illustrates an example of a foldable tablet terminal (in an openstate). A tablet terminal 7500 includes a housing 7501 a, a housing 7501b, a display portion 7502 a, and a display portion 7502 b. The housing7501 a and the housing 7501 b are connected by a hinge 7503 and can beopened and closed along the hinge 7503. The housing 7501 a includes apower switch 7504, operation keys 7505, a speaker 7506, and the like.Note that the tablet terminal 7500 is manufactured using thelight-emitting device according to one embodiment of the presentinvention for either the display portion 7502 a or the display portion7502 b, or both of them.

Part of the display portion 7502 a or the display portion 7502 b, inwhich data can be input by touching displayed operation keys can be usedas a touch panel region. For example, the entire area of the displayportion 7502 a can display keyboard buttons and serve as a touch panelwhile the display portion 7502 b can be used as a display screen.

An indoor lighting device 7601, a roll-type lighting device 7602, a desklamp 7603, and a planar lighting device 7604 illustrated in FIG. 9A areeach an example of a lighting device which includes the light-emittingdevice of one embodiment of the present invention. Since thelight-emitting device of an embodiment of the present invention can alsohave a larger area, the light-emitting device of an embodiment of thepresent invention can be used as a lighting system having a large area.Further, since the light-emitting device is thin, the light-emittingdevice can be mounted on a wall.

A desk lamp illustrated in FIG. 9B includes a lighting portion 7701, asupport 7703, a support base 7705, and the like. The light-emittingdevice of one embodiment of the present invention is used for thelighting portion 7701. In one embodiment of the present invention, alighting device whose light-emitting portion has a curved surface or alighting device including a flexible lighting portion can be achieved.Such use of a flexible light-emitting device for a lighting deviceenables a place having a curved surface, such as the ceiling ordashboard of a motor vehicle, to be provided with the lighting device,as well as increases the degree of freedom in design of the lightingdevice.

Note that this embodiment can be combined with any of other embodiments,as appropriate.

Example 1

In Example 1, a light-emitting device which is one embodiment of thepresent invention is described with reference. In this example, atop-emission light-emitting device was manufactured. FIGS. 10A and 10Bare plan views of the light-emitting device manufactured in thisexample. FIG. 11A is a cross-sectional view taken along dashed-dottedline X1-Y1 in FIG. 10A. FIG. 11B is a cross-sectional view taken alongdashed-dotted line X2-Y2 in FIG. 10B. Note that some components of thelight-emitting device are omitted in FIGS. 10A and 10B.

<Structure of Light-Emitting Device>

First, structures of light-emitting devices 1 to 4 manufactured in thisexample will be described. Table 1 shows the type of a supportingsubstrate of each light-emitting device, the area of a light-emittingregion of each light-emitting device, and the presence or absence of alight extraction structure.

TABLE 1 Light Supporting Light-emitting extraction substrate regionstructure Light-emitting device 1 Glass 56 mm × 42 mm noneLight-emitting device 2 provided Light-emitting device 3 Stainless steelprovided Light-emitting device 4 Glass 2 mm × 2 mm none

The structure of the light-emitting device in FIG. 11A corresponds tothe structure of the light-emitting device 2, and the structure except alight extraction structure 1109 corresponds to the structures of thelight-emitting devices 1 and 4 (note that the area of a light-emittingregion is different between the light-emitting devices 1 and 4).Specifically, in each of the light-emitting devices 1 and 4, alight-emitting element 1150 is provided over a supporting substrate 1100with an insulating film 1104 interposed therebetween. The light-emittingelement 1150 includes a first electrode 1101, an EL layer 1102, and asecond electrode 1103. An end portion of the first electrode 1101 and anend portion of a terminal 1110 are covered with a partition wall 1105.The terminal 1110 is electrically connected to the second electrode1103. In addition, an auxiliary wiring 1106 is provided over the firstelectrode 1101 with the partition wall 1105 provided therebetween, andis electrically connected to the second electrode 1103. The supportingsubstrate 1100 and a sealing substrate 1108 are bonded with a sealingmaterial 1107. In the light-emitting device 2, the light extractionstructure 1109 is bonded to the surface of the sealing substrate 1108.

The cross-sectional view of the light-emitting device in FIG. 11Bcorresponds to the cross-sectional view of the light-emitting device 3.Specifically, in the light-emitting device 3, the light-emitting element1150 is provided over a supporting substrate 1120 with an insulatingfilm 1124 interposed therebetween. The end portion of the firstelectrode 1101 and the end portion of the terminal 1110 are covered witha partition wall 1125. The terminal 1110 is electrically connected tothe second electrode 1103. In addition, the auxiliary wiring 1106 isprovided over the first electrode 1101 with the partition wall 1125provided therebetween, and is electrically connected to the secondelectrode 1103. The supporting substrate 1120 and a sealing substrate1128 are bonded with the sealing material 1107. Further, the lightextraction structure 1109 is bonded to the surface of the sealingsubstrate 1128. In the light-emitting device 3 of this example, a thinstainless steel substrate was used as the supporting substrate 1120, anda substrate including a thin glass layer and a polyethyleneterephthalate (PET) layer was used as the sealing substrate 1128. Thesesubstrates are flexible, and the light-emitting device 3 is a flexiblelight-emitting device.

A specific structure of the light-emitting element 1150 included in thelight-emitting devices 1 to 4 is shown in FIG. 18A. The light-emittingelement 1150 includes the first electrode 1101, the EL layer 1102 overthe first electrode 1101, and the second electrode 1103 over the ELlayer 1102. The EL layer 1102 includes a hole-injection layer 1111 overand in contact with the first electrode 1101, a hole-transport layer1112 over and in contact with the hole-injection layer 1111, a firstlight-emitting layer 1113 a over and in contact with the hole-transportlayer 1112, a second light-emitting layer 1113 b over and in contactwith the first light-emitting layer 1113 a, a third light-emitting layer1113 c over and in contact with the second light-emitting layer 1113 b,an electron-transport layer 1114 over and in contact with the thirdlight-emitting layer 1113 c, and an interlayer 1116 over and in contactwith the electron-transport layer 1114.

<Manufacturing Method of Light-Emitting Device>

Next, a method for manufacturing the light-emitting devices 1 to 4 isdescribed.

<Light-Emitting Device 1>

First, a 100-nm-thick silicon oxynitride film was deposited by a CVDmethod to form the insulating film 1104 over a 0.7-mm-thick glasssubstrate which was the supporting substrate 1100.

Next, a 50-nm-thick titanium film was formed by a sputtering method.Then, a 200-nm-thick aluminum-nickel alloy film containing lanthanum(Al—Ni—La) was formed by a sputtering method. In addition, a 3-nm-thicktitanium film was formed by a sputtering method. Then, heat treatmentwas performed in a nitrogen atmosphere at 250° C. for one hour. A10-nm-thick indium tin oxide film containing silicon oxide (ITSO) wasformed by a sputtering method. Thus, the first electrode 1101 serving asan anode was formed.

Next, in order to form a 1-μm-thick partition wall 1105, photosensitivepolyimide was applied, exposed to light, and developed. After that, heattreatment was performed in a nitrogen atmosphere at 250° C. for onehour. Note that seven partition walls 1105 each having a width L1 of 330μm were formed over the first electrode 1101.

Next, seven auxiliary wirings 1106 were formed using silver paste overthe partition walls 1105 by a printing method. At this time, the pitchof the auxiliary wirings 1106 was 5.3 mm and the width L2 was 100 μm.Then, heat treatment was performed in an air atmosphere at 200° C. for80 minutes.

Next, as pretreatment for forming the EL layer 1102, UV-ozone treatmentwas performed for 370 seconds after washing of a surface of thesupporting substrate 1100 with water and baking that was performed at200° C. for 1 hour.

After that, the supporting substrate 1100 was transferred into a vacuumevaporation apparatus where the pressure had been reduced toapproximately 10⁻⁴ Pa, and subjected to vacuum baking at 170° C. for 30minutes in a heating chamber of the vacuum evaporation apparatus, andthen the supporting substrate 1100 was cooled down for about 30 minutes.

Next, an EL layer 1102 in which a plurality of layers were stacked wasformed over the first electrode 1101. Chemical formulae of materialsused for the EL layer 1102 are shown below.

First, the supporting substrate 1100 provided with the first electrode1101 was fixed to a substrate holder in the vacuum evaporation apparatusso that a surface on which the first electrode 1101 was provided faceddownward. The pressure in the vacuum evaporation apparatus was reducedto about 10⁻⁴ Pa. Then,4,4′,4″-(1,3,5-benzenetriyl)tri(dibenzothiophene) (abbreviation:DBT3P-II) and molybdenum oxide were deposited by co-evaporation to formthe hole-injection layer 1111 over the first electrode 1101. Thethickness was 20 nm, and the weight ratio of DBT3P-II to molybdenumoxide was adjusted to 2:1 (=DBT3P-II:molybdenum oxide). Note that theco-evaporation refers to an evaporation method in which vapor depositionis carried out from a plurality of evaporation sources at the same timein one treatment chamber.

Next, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1) were deposited by co-evaporation, whereby thehole-transport layer 1112 was formed on the hole-injection layer 1111.The thickness was 20 nm and the weight ratio of BPAFLP to PCzPCN1 wasadjusted to 1:1 (=BPAFLP:PCzPCN1).

Further,2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II), PCzPCN1 and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) were deposited by co-evaporation toform the first light-emitting layer 1113 a over the hole-transport layer1112. Here, the weight ratio of 2mDBTBPDBq-II, PCzPCN1, and[Ir(tBuppm)₂(acac)] was adjusted to 0.7:0.3:0.06(=2mDBTBPDBq-II:PCzPCN1:[Ir(tBuppm)₂(acac)]). The thickness of the firstlight-emitting layer 1113 a was set to 12 nm.

Next, 2mDBTBPDBq-II, PCzPCN1, and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]) were deposited on the hole-transportlayer 1112 by co-evaporation, whereby the second light-emitting layer1113 b was formed over the first light-emitting layer 1113 a. Here, theweight ratio of 2mDBTBPDBq-II, PCzPCN1, and [Ir(dppm)₂(acac)] wasadjusted to 0.8:0.2:0.06 (=2mDBTBPDBq-II:PCzPCN1:[Ir(dppm)₂(acac)]). Inaddition, the thickness of the second light-emitting layer 1113 b wasset to 18 nm.

Then, 9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation:CzPA) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6 mMemFLPAPrn) were deposited by co-evaporation,whereby the third light-emitting layer 1113 c was formed over the secondlight-emitting layer 1113 b. The thickness was 10 nm. The weight ratioof CzPA to 1,6 mMemFLPAPrn was adjusted to 1:0.05 (=CzPA:1,6mMemFLPAPrn).

Next, CzPA was vapor-deposited to a thickness of 5 nm and thenbathophenanthroline (abbreviation: BPhen) was vapor-deposited to athickness of 10 nm, so that the electron-transport layer 1114 was formedover the third light-emitting layer 1113 c.

Further, lithium oxide (Li₂O) was vapor-deposited to a thickness of 0.1nm, copper phthalocyanine (abbreviation: CuPc) was vapor-deposited to athickness of 1 nm, and DBT3P-II and molybdenum oxide were deposited to athickness of 100 nm by co-evaporation, so that the interlayer 1116 wasformed over the electron-transport layer 1114. Note that the thicknessthe weight ratio of DBT3P-II to molybdenum oxide was adjusted to 2:1(=DBT3P-II:molybdenum oxide).

Finally, in order to form the second electrode 1103 serving as acathode, indium tin oxide (ITO) was vapor-deposited to a thickness of110 nm.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 2 shows the element structure of the light-emitting elementobtained as described above.

TABLE 2 Hole- injec- Hole- Electron- 2nd 1st tion transport 1st light-2nd light- 3rd light- transport elec- electrode layer layer emittinglayer emitting layer emitting layer layer Interlayer trode Ti * ITSODBT3P- BPAFLP: 2mDBTBPDBq- 2mDBTBPDBq- CzPA: CzPA BPhen Li₂O CuPc DBT3P-ITO 50 10 II: PCzPCN1 II:PCzPCN1: II:PCzPCN1: 1,6mMemFLPAPrn 5 10 0.1 1II:MoOx 110 nm nm MoOx (=1:1) [Ir(tBuppm)₂(acac)] [Ir(dppm)₂(acac)](=1:0.05) nm nm nm nm (=2:1) nm (=2:1) 20 nm (=0.7:0.3:0.06)(=0.8:0.2:0.06) 10 nm 100 nm 20 nm 12 nm 18 nm * Light-emitting devices1, 2, and 4: Al—Ni—La (200 nm)\Ti (3 nm), Light-emitting device 3: APC(200 nm)

Next, the supporting substrate 1100 and a glass substrate which is thesealing substrate 1108 were bonded using an ultraviolet curable epoxyresin which is the sealing material 1107. After that, heat treatment wasperformed in an air atmosphere at 80° C. for one hour.

<Light-Emitting Device 2>

A method for manufacturing the light-emitting device 2 includes stepssimilar to those in the manufacturing method of the light-emittingdevice 1 and also includes a lens diffusion plate (product name:LSD60PC10-F12, produced by Optical Solutions Corporation) which was thelight extraction structure 1109 was bonded to the surface of the sealingsubstrate 1108 using an ultraviolet curable epoxy resin.

<Light-Emitting Device 3>

First, as pretreatment, UV ozone treatment was performed to a stainlesssteel substrate (thickness of 100 μm), which is the supporting substrate1120, for 10 minutes. Next, the insulating film 1124 was formed over thesupporting substrate 1120 using a heat-resistance polyamide-imide-basedresin. Then, heat treatment was performed in an air atmosphere at 130°C. for 10 minutes and at 270° C. for 30 minutes.

Next, in order to form the first electrode 1101 serving as an anode, a50-nm-thick titanium film was formed by a sputtering method, a200-nm-thick copper-palladium-copper alloy (also referred to as APC)film was formed by a sputtering method, and further a 10-nm-thick ITSOfilm was formed by a sputtering method.

Then, fourteen partition walls 1125 each having a width L1 of 400 μmwere formed over the first electrode 1101 using a thermal curable epoxyresin by a printing method. After the first printing, heat treatment wasperformed under an air atmosphere at 150° C. for 10 minutes, and thensecond printing was performed. Then, heat treatment was performed in anair atmosphere at 200° C. for 80 minutes. Further, at the same time, apartition wall 1125 covering an end portion of the first electrode 1101and an end portion of the terminal 1110 was formed over the insulatingfilm 1124.

Next, fourteen auxiliary wiring 1106 each having a width L2 of 200 μmwere formed over the partition walls 1125 using silver paste by aprinting method. The pitch of the auxiliary wiring 1106 was 3 mm. Then,heat treatment was performed in an air atmosphere at 200° C. for 80minutes.

Next, the EL layer 1102 and the second electrode 1103 were fainted overthe first electrode 1101 in the conditions similar to those of thelight-emitting device 1.

Next, the supporting substrate 1120 and the substrate including a thinglass layer and a polyethylene terephthalate (PET) layer which was thesealing substrate 1128 were bonded using a UV curable epoxy resin whichwas the sealing material 1107. Then, in order to cure the sealingmaterial 1107, UV light irradiation was performed for 120 seconds. Next,heat treatment was performed in an air atmosphere at 80° C. for onehour. Then, the lens diffusion plate (product name: LSD60PC10-F12,produced by Optical Solutions Corporation) which was the lightextraction structure 1109 was bonded to the surface of the sealingsubstrate 1128 using an ultraviolet curable epoxy resin.

<Light-Emitting Device 4>

A manufacturing method of the light-emitting device 4 is similar to thatof the light-emitting device 1.

<Characteristics of Light-Emitting Device>

Table 3 shows initial values of main characteristics of thelight-emitting devices 1 to 3 at a current density of 0.45 mA/cm² andthe light-emitting device 4 at a current density of 2.5 mA/cm².

TABLE 3 Correlated External color Power quantum Voltage Chromaticitytemperature efficiency efficiency (V) (x, y) (K) (lm/W) (%) Light- 2.57(0.48, 0.51) 3100 74 19 emitting device 1 Light- 2.57 (0.50, 0.50) 2800100 27 emitting device 2 Light- 2.54 (0.50, 0.49) 2800 92 25 emittingdevice 3 Light- 2.80 (0.50, 0.50) 2800 87 26 emitting device 4

In the light-emitting element of this example, the green-light-emittingphosphorescent compound, the orange-light-emitting phosphorescentcompound, and the blue-light-emitting fluorescent compound were used aslight-emitting substances. Adjustment of emission balance among thephosphorescent and fluorescent light-emitting layers could increaseemission efficiency of the light-emitting element.

In the light-emitting element of this example, the electron-transportorganic compound is used as a host material of the blue-light-emittingfluorescent compound and is positioned to be the closest to the cathodeamong the three light-emitting layers; with this structure, lightemission from the phosphorescent compounds is easily obtained.Accordingly, the light-emitting element with high emission efficiencywas achieved.

Although light emitted from a fluorescent compound is weaker than thatfrom a phosphorescent compound, the light-emitting element of thisexample is preferable particularly in the case where a strong blueemission is unnecessary and high emission efficiency is required, forexample, for a warm-white light-emitting device used as lighting.

The power efficiency of the light-emitting device 2 was 100 lm/W, whichwas about 1.4 times as high as that of the light-emitting device 1. Thisis because the light extraction efficiency was increased owing to thelight extraction structure 1109 included in the light-emitting device 2.Further, the light-emitting device 3, which is flexible, shows favorableperformance equivalent to that of the light-emitting device 2manufactured over the glass substrate.

Results of the reliability test of the light-emitting device 4 are shownin FIG. 12. In FIG. 12, the vertical axis represents normalizedluminance (%) on the assumption that the initial luminance is 100%, andthe horizontal axis represents driving time (h) of the elements. In thereliability test, the light-emitting element 4 was driven at roomtemperature under the conditions where the initial luminance was set to5000 cd/m² and the current density was constant. This corresponds to aninitial luminance of 7000 cd/m² when the light extraction structure 1109is provided. The half decay time of luminance at an initial luminance of1,000 cd/m² is 100,000 hours by the estimation based on the results ofFIG. 12, which is a favorable driving lifetime.

[Reflective Electrode]

In a top-emission light-emitting device, an aluminum alloy or the likecan be used as a reflective electrode (the lower electrode and the firstelectrode 1101) of the light-emitting element. An aluminum alloy ispreferably used for the following reasons: it is inexpensive, it has ahigh reflectance, it is easily processed, and the like. On the otherhand, in terms of carrier injection into a light-emitting element (ELlayer), a transparent oxide conductive material such as ITO and ITSO issuperior to an aluminum alloy. However, it is not preferable thataluminum and a transparent conductive material have direct contactbecause they might corrode. Thus, a thin titanium film was providedbetween an Al—Ni—La film and an ITSO film in this example. A titaniumfilm is easily oxidized and thus becomes a titanium oxide film by oxygenin the air, heat treatment after the titanium film is deposited, or thelike. Since a titanium oxide is stable in the air and has conductivity,it does not prevent hole injection into the light-emitting element (ELlayer). Further, a problem such as corrosion does not occur if atransparent oxide conductive film is formed over a titanium film.Further, a titanium oxide film has a transmitting property with respectto visible light. As shown in FIG. 13, since the reflectance of thefirst electrode 1101 used in this example is 80% or more in a visiblelight region, the electrode can be preferably used as a reflectiveelectrode of a light-emitting element.

[Interlayer]

In a top-emission light-emitting device, an upper electrode of alight-emitting element needs to have a transmitting property withrespect to visible light. Therefore, ITO was used for the secondelectrode 1103 in this example. Further, when the interlayer 1116 whichis in contact with the second electrode 1103 is provided as in thelight-emitting device of this example, an excellent carrier injectionproperty from ITO can be obtained. Further, sputtering damage to the ELlayer 1102 at the time of ITO deposition can be reduced.

[Substrate]

A metal substrate such as an aluminum substrate or a stainless steelsubstrate has higher heat dissipation property than a glass substrateand thus easily dissipates heat generated from a light-emitting element.The reliability of a light-emitting element is easily lowered due todecrease in lifetime and increase in percentage of defects caused byhigh temperature.

Here, light-emitting elements were manufactured over a glass substrateand an aluminum substrate under the same conditions. FIG. 14 showsresults of measuring surface temperatures in the center of the elementsusing a thermocouple when a constant current was kept being flown underroom temperature. FIG. 15A shows results of temperature distributions onthe surface of the element over the glass substrate at 300 seconds afterthe start of the driving. FIG. 15B shows results of temperaturedistributions on the surface of the element over the aluminum substrateafter 300 seconds of start of the driving. These temperatures weremeasured under room temperature.

From the results, the surface temperature of the light-emitting elementmanufactured over the aluminum substrate is, in the entire region, lowerthan that of the light-emitting element manufactured over the glasssubstrate; in the center of the element where the temperature tends toincrease particularly, the surface temperature was lower by about 10° C.The results show that a highly reliable light-emitting device can bemanufactured using a metal substrate. The results also show that ahighly reliable flexible light-emitting device can be manufactured usinga thin and flexible metal substrate as in the light-emitting device 3 ofthis example. Note that it has been confirmed that, the light-emittingdevice in which the metal substrate has a thickness of 200 μm is notbroken and stable light emission can be obtained if the light-emittingdevice is bent to a radius curvature of 21 mm.

Example 2

In Example 2, a light-emitting device which is one embodiment of thepresent invention is described. In this example, a bottom-emissionlight-emitting device was manufactured. FIGS. 10C and 10D are plan viewsof the light-emitting device manufactured in this example. FIG. 16A is across-sectional view taken along dashed-dotted line X3-Y3 in FIG. 10C.FIG. 11B is a cross-sectional view taken along dashed-dotted line X4-Y4in FIG. 10D. Note that some components of the light-emitting device areomitted in FIGS. 10C and 10D.

<Structure of Light-Emitting Device>

First, structures of light-emitting devices 5 to 9 manufactured in thisexample will be described. Table 4 shows the type of a supportingsubstrate of each light-emitting device, the area of a light-emittingregion of each light-emitting device, and the presence or absence of alight extraction structure.

TABLE 4 Light-emitting Light exraction Substrate region structureLight-emitting device 5 Glass 56 mm × 42 mm none Light-emitting device 6provided Light-emitting device 7 PEN film provided Light-emitting device8 Glass 2 mm × 2 mm none Light-emitting device 9 PEN film none

The structure of the light-emitting device in FIG. 16A corresponds tothe structure of the light-emitting device 6, and the structure except alight extraction structure 1209 corresponds to the structures of thelight-emitting devices 5 and 8 (note that the area of a light-emittingregion is different between the light-emitting devices 5 and 8).Specifically, in each of the light-emitting devices 5 and 8, alight-emitting element 1250 is provided over a supporting substrate 1200with an insulating film 1204 interposed therebetween. The light-emittingelement 1250 includes a first electrode 1201, an EL layer 1202, and asecond electrode 1203. The auxiliary wiring 1206 is provided over theinsulating film 1204 and is electrically connected to the firstelectrode 1201. An end portion of the first electrode 1201 and an endportion of a terminal 1210 are covered with a partition wall 1205.Further, the partition wall 1205 is provided to cover the auxiliarywiring 1206 with the first electrode 1201 provided therebetween. Thesupporting substrate 1200 and a sealing substrate 1208 are bonded with asealing material 1207. In the light-emitting device 6, the lightextraction structure 1209 is bonded to the surface of the supportingsubstrate 1200.

The cross-sectional view of the light-emitting device in FIG. 16Bcorresponds to that of the light-emitting device 7, and the structureexcept the light extraction structure 1209 corresponds to the structuresof the light-emitting device 9 (note that the area of a light-emittingregion is different between the light-emitting devices 7 and 9).Specifically, in the light-emitting device 9, the light-emitting element1250 is provided over a supporting substrate 1220 with an insulatingfilm 1224 interposed therebetween. The auxiliary wiring 1206 is providedover the insulating film 1224 and is electrically connected to the firstelectrode 1201. The end portion of the first electrode 1201 and the endportion of the terminal 1210 are covered with the partition wall 1205.Further, the partition wall 1205 is provided to cover the auxiliarywiring 1206 with the first electrode 1201 provided therebetween. Thesupporting substrate 1220 and a sealing substrate 1228 are bonded with asealing material 1227. In the light-emitting device 7, the lightextraction structure 1209 is bonded to the surface of the supportingsubstrate 1220. In the light-emitting devices 7 and 9 of this example, apolyethylene naphthalate (PEN) film substrate and a thin stainless steelsubstrate were used as the supporting substrate 1220 and the sealingsubstrate 1228, respectively. These substrates are flexible, and thelight-emitting devices 7 and 9 are flexible light-emitting devices.

A specific structure of the light-emitting element 1250 included in thelight-emitting devices 5 to 9 is shown in FIG. 18B. The light-emittingelement 1250 includes the first electrode 1201, the EL layer 1202 overthe first electrode 1201, and the second electrode 1203 over the ELlayer 1202. The EL layer 1202 includes a hole-injection layer 1211 overand in contact with the first electrode 1201, a hole-transport layer1212 over and in contact with the hole-injection layer 1211, a firstlight-emitting layer 1213 a over and in contact with the hole-transportlayer 1212, a second light-emitting layer 1213 b over and in contactwith the first light-emitting layer 1213 a, a third light-emitting layer1213 c over and in contact with the second light-emitting layer 1213 b,an electron-transport layer 1214 over and in contact with the thirdlight-emitting layer 1213 c, and an electron-injection layer 1215 overand in contact with the electron-transport layer 1214.

<Manufacturing Method of Light-Emitting Device>

Next, a manufacturing method of the light-emitting devices 5 to 9 isdescribed.

<Light-Emitting Device 5>

First, a 100-nm-thick silicon oxynitride film was deposited by a CVDmethod to form the insulating film 1204 over a 0.7-mm-thick glasssubstrate which was the supporting substrate 1200.

Next, a 100-nm-thick titanium film was formed by a sputtering method, a1000-nm-thick aluminum film was formed by a sputtering method, and thena 100-nm-thick titanium film was formed by a sputtering method, wherebyseven auxiliary wirings 1206 were formed. At this time, the pitch of theauxiliary wirings 1206 was 5.3 mm and the width L4 was 322 μm.

Next, an ITSO film was formed over the supporting substrate 1200 and theauxiliary wirings 1206 by a sputtering method, so that the firstelectrode 1201 serving as an anode was formed. Note that the thicknesswas 110 nm.

Next, in order to form the partition wall 1205 with a thickness of 1.5μm, photosensitive polyimide was applied, exposed to light, anddeveloped. After that, heat treatment was performed in a nitrogenatmosphere at 250° C. for one hour. Note that seven partition walls 1205covering the auxiliary wirings 1206 were formed to have a width L3 of330 μm.

Next, as pretreatment for forming the EL layer 1202, UV-ozone treatmentwas performed for 370 seconds after washing of a surface of thesupporting substrate 1200 with water and baking that was performed at200° C. for 1 hour.

After that, the supporting substrate 1200 was transferred into a vacuumevaporation apparatus where the pressure had been reduced toapproximately 10⁻⁴ Pa, and subjected to vacuum baking at 170° C. for 30minutes in a heating chamber of the vacuum evaporation apparatus, andthen the supporting substrate 1200 was cooled down naturally for about30 minutes.

Next, an EL layer 1202 was formed over the first electrode 1201.Chemical formulae of materials used for the EL layer 1202 are shownbelow. Note that the materials the chemical formulae of which aredescribed above will be omitted.

Then, the supporting substrate 1200 over which the first electrode 1201was formed was fixed to a substrate holder provided in the vacuumevaporation apparatus so that the surface on which the first electrode1201 was formed faced downward. The pressure in the vacuum evaporationapparatus was reduced to about 10⁻⁴ Pa. After that, over the firstelectrode 1201, DBT3P-II and molybdenum oxide were deposited byco-evaporation by an evaporation method using resistance heating, sothat the hole-injection layer 1211 was formed over the first electrode1201. The thickness was 30 nm, and the weight ratio of DBT3P-II tomolybdenum oxide was adjusted to 2:1 (=DBT3P-II:molybdenum oxide).

Next, in order to form the hole-transport layer 1212 over thehole-injection layer 1211, BPAFLP was vapor-deposited to a thickness of20 nm.

Further, the first light-emitting layer 1213 a was formed over thehole-transport layer 1212 by co-evaporation of 2mDBTBPDBq-II,4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB), and [Ir(tBuppm)₂(acac)]. Here, the weight ratioof 2mDBTBPDBq-II to PCBNBB to [Ir(tBuppm)₂(acac)] was adjusted to0.7:0.3:0.06 (=2mDBTBPDBq-II:PCBNBB:[Ir(tBuppm)₂(acac)]). The thicknessof the first light-emitting layer 1213 a was set to 8 nm.

Next, 2mDBTBPDBq-II, PCBNBB, and [Ir(dppm)₂(acac)]) were deposited byco-evaporation, whereby the second light-emitting layer 1213 b wasformed over the first light-emitting layer 1213 a. Here, the weightratio of 2mDBTBPDBq-II, PCBNBB, and [Ir(dppm)₂(acac)] was adjusted to0.8:0.2:0.06 (=2mDBTBPDBq-II:PCBNBB:[Ir(dppm)₂(acac)]). In addition, thethickness of the second light-emitting layer 1213 b was set to 22 nm.

Then, in order to form the third light-emitting layer 1213 c over thesecond light-emitting layer 1213 b, CzPA and 1,6 mMemFLAPAPrn weredeposited to a thickness of 10 nm by co-evaporation. The weight ratio ofCzPA to 1,6 mMemFLPAPrn was adjusted to 1:0.05 (=CzPA:1,6 mMemFLPAPrn).

Next, CzPA was vapor-deposited to a thickness of 5 nm and then BPhen wasvapor-deposited to a thickness of 15 nm, so that the electron-transportlayer 1214 was formed over the third light-emitting layer 1213 c.

Further, in order to form the electron-injection layer 1215 over theelectron-transport layer 1214, lithium fluoride (LiF) wasvapor-deposited to a thickness of 1 nm.

Finally, in order to fount the second electrode 1203 serving as acathode, silver (Ag) and magnesium (Mg) were deposited to a thickness of1 nm by co-evaporation and further silver (Ag) was vapor-deposited to athickness of 200 nm. Here, the volume ratio of Ag to Mg was adjusted to2:1 (=Ag:Mg).

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

The element structure of the light-emitting element obtained asdescribed above is shown in Table 5.

TABLE 5 Hole- Hole- Electron- Electron- 1st injection transport 1stlight- 2nd light- 3rd light- transport injection 2nd electrode layerlayer emitting layer emitting layer emitting layer layer layer electrodeITSO DBT3P-II: BPAFLP 2mDBTBPDBq-II: 2mDBTBPDBq-II: CzPA: CzPA BPhen LiFAg:Mg Ag 110 nm MoOx 20 nm PCBNBB: PCBNBB: 1,6mMemFLPAPrn 5 nm 15 nm 1nm (=2:1) 200 nm (=2:1) [Ir(tBuppm)₂(acac)] [Ir(dppm)₂(acac)] (=1:0.05)1 nm 30 nm (=0.7:0.3:0.06) (=0.8:0.2:0.06) 10 nm 8 nm 22 nm

Next, the supporting substrate 1200 and a glass substrate which is thesealing substrate 1208 were bonded using an ultraviolet curable epoxyresin which is the sealing material 1207. After that, heat treatment wasperformed in an air atmosphere at 80° C. for one hour.

In addition, in order to cure the sealing material 1207, UV lightirradiation was performed for 60 seconds.

<Light-Emitting Device 6>

A method for manufacturing the light-emitting device 6 includes stepssimilar to those in the manufacturing method of the light-emittingdevice 5 and also includes a lens diffusion plate (product name:LSD60PC10-F12, produced by Optical Solutions Corporation) which was thelight extraction structure 1209 was bonded to the surface of thesupporting substrate 1200 using an ultraviolet curable epoxy resin.

<Light-Emitting Device 7>

The light-emitting device 7 was manufactured by employing themanufacturing method A (FIGS. 4A to 4E) of a light-emitting device,which was described in Embodiment 3. First, a 100-nm-thick siliconoxynitride film was formed as a base film over a glass substrate servingas the formation substrate 601. Then, washing was performed using ahydrogen fluoride aqueous solution of 0.5%. This step leads toimprovement in adhesion between the base film and the separation layer603 to be formed later.

Next, a 30-nm-thick tungsten film was formed over the base film as theseparation layer 603, and the layer 605 was formed over the separationlayer 603. The layer 605 in this example includes the insulating film1224, the auxiliary wiring 1206, the first electrode 1201, and thepartition wall 1205.

As the layer 605, first, the insulating film 1224 was formed over theseparation layer 603. For the insulating film 1224, a 600-nm-thicksilicon oxynitride film, a 200-nm-thick silicon nitride film, a200-nm-thick silicon oxynitride film, a 140-nm-thick silicon nitrideoxide film, and a 100-nm-thick silicon oxynitride film were stacked inthis order. After that, heat treatment was performed at 480° C. in anitrogen atmosphere for one hour.

Next, the auxiliary wiring 1206, the first electrode 1201, and thepartition wall 1205 were formed in conditions similar to those in thelight-emitting device 5.

Then, a UV curable adhesive film (also referred to as UV film) servingas the temporary supporting substrate 607 and the first electrode 1201were bonded using a water-soluble resin serving as the separationadhesive 609. Then, the layer 605 is separated from the formationsubstrate 601 along the separation layer 603. Thus, the layer 605 isprovided on the temporary supporting substrate 607 side.

Note that in order to easily separate the separation layer 603 from thelayer 605, laser light irradiation with a UV laser was performed in thisexample.

Next, the layer 605 which was separated from the formation substrate 601and includes the exposed insulating film 1224 (a layer included in theinsulating film 1224) was bonded to the supporting substrate 1220 usinga UV curable adhesive. A 100-μm-thick polyethylene naphthalate (PEN)film was used as the supporting substrate 1220. The UV curable adhesivewas cured by UV light irradiation for 10 minutes, and then, theseparation adhesive 609 was removed by washing with water.

Next, the EL layer 1202 and the second electrode 1203 were formed overthe first electrode 1201 in the conditions similar to those in thelight-emitting device 5.

Then, a photocurable resin containing zeolite which serves as thesealing material 1227 was applied and cured by UV light irradiation for120 seconds. Further, heat treatment was performed at 80° C. under anair atmosphere for one hour. Then, the supporting substrate 1220 and thethin stainless steel substrate which was the sealing substrate 1228 werebonded with a two component type epoxy resin. Then, the lens diffusionplate (product name: LSD60PC10-F12, produced by Optical SolutionsCorporation) which was the light extraction structure 1209 was bonded tothe surface of the supporting substrate 1220 using an ultravioletcurable epoxy resin.

<Light-Emitting Device 8>

A manufacturing method of the light-emitting device 8 is similar to thatof the light-emitting device 5.

<Light-Emitting Device 9>

A manufacturing method of the light-emitting device 9 is similar to thatof the light-emitting device 7. Note that the light extraction structure1209 was not provided in the light-emitting device 9.

<Characteristics of Light-Emitting Device>

Table 6 shows initial values of main characteristics of thelight-emitting devices 5 to 7 at a current density of 0.45 mA/cm² andthe light-emitting devices 8 and 9 at a current density of 2.5 mA/cm².

TABLE 6 Correlated External color Power quantum Voltage Chromaticitytemperature efficiency efficiency (V) (x, y) (K) (lm/W) (%) Light- 2.66(0.52, 0.47) 2400 88 25 emitting device 5 Light- 2.66 (0.52, 0.48) 2500122 35 emitting device 6 Light- 2.76 (0.52, 0.48) 2500 110 33 emittingdevice 7 Light- 3.16 (0.52, 0.49) 2500 94 31 emitting device 8 Light-3.01 (0.51, 0.49) 2700 98 30 emitting device 9

In the light-emitting element of this example, the green-light-emittingphosphorescent compound, the orange-light-emitting phosphorescentcompound, and the blue-light-emitting fluorescent compound were used aslight-emitting substances. Adjustment of emission balance among thephosphorescent and fluorescent light-emitting layers could increaseemission efficiency of the light-emitting element.

In the light-emitting element of this example, the electron-transportorganic compound is used as a host material of the blue-light-emittingfluorescent compound and is positioned to be the closest to the cathodeamong the three light-emitting layers; with this structure, lightemission from the phosphorescent compounds is easily obtained.Accordingly, the light-emitting element with high emission efficiencywas achieved.

Although light emitted from a fluorescent compound is weaker than thatfrom a phosphorescent compound, the light-emitting element of thisexample is preferable particularly in the case where a strong blueemission is unnecessary and high emission efficiency is required, forexample, for a warm-white light-emitting device used as lighting.

The power efficiency of the light-emitting device 6 was 122 lm/W, whichwas about 1.4 times as high as that of the light-emitting device 5. Thisis because the light extraction efficiency was increased owing to thelight extraction structure 1209 included in the light-emitting device 6.Further, the light-emitting device 7, which is flexible, shows favorableperformance equivalent to that of the light-emitting device 6manufactured over the glass substrate. Note that it has been confirmedthat, the light-emitting device in which the film substrate using resinhas a thickness of 20 μm is not broken and stable light emission can beobtained if the light-emitting device is bent to a radius curvature of10 mm.

Results of the reliability test of the light-emitting devices 8 and 9are shown in FIG. 17. In FIG. 17, the vertical axis representsnormalized luminance (%) on the assumption that the initial luminance is100%, and the horizontal axis represents driving time (h) of theelements. In the reliability tests, the light-emitting devices weredriven at room temperature under the conditions where the initialluminance was set to 5000 cd/m² and the current density was constant.This corresponds to an initial luminance of 7000 cd/m² when the lightextraction structure 1209 is provided. It was found from FIG. 17 thatthe lifetime of the light-emitting device 8 overlaps with that of thelight-emitting device 9 and thus there is little difference betweentheir reliabilities. The half decay time of luminance at an initialluminance of 1,000 cd/m² is 300,000 hours by the estimation based on theresults of FIG. 17, which is a favorable driving lifetime.

Example 3

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIGS. 18C and 18D.Chemical formulas of materials used in this example are shown below.Note that the materials the chemical formulae of which are describedabove will be omitted.

As shown in FIG. 18C, the light-emitting element 1 of this exampleincludes an EL layer 2002 a between a first electrode 2001 and a secondelectrode 2003. The EL layer 2002 a includes a hole-injection layer2011, a hole-transport layer 2012, a first light-emitting layer 2013 a,a second light-emitting layer 2013 b, a third light-emitting layer 2013c, an electron-transport layer 2014, and an electron-injection layer2015, which are stacked in this order.

As shown in FIG. 18D, the light-emitting element 2 of this exampleincludes an EL layer 2002 b between the first electrode 2001 and thesecond electrode 2003. The EL layer 2002 b includes the hole-injectionlayer 2011, the hole-transport layer 2012, the first light-emittinglayer 2013 a, the second light-emitting layer 2013 b, the thirdlight-emitting layer 2013 c, the electron-transport layer 2014, and theelectron-injection layer 2015, which are stacked in this order.

The manufacturing method of the light-emitting element 1 will bedescribed. Note that the manufacturing method of the light-emittingdevice 2 is similar to that of the light-emitting device 1 except thatthe first light-emitting layer 2013 a and the second light-emittinglayer 2013 b are formed in reverse order; therefore, specificdescription is omitted.

First, an ITSO film was formed over a glass substrate serving as asupporting substrate by a sputtering method, so that a first electrode2001 serving as an anode was formed. The thickness was 110 nm and theelectrode area was 2 mm×2 mm.

In pretreatment for forming the light-emitting element over the glasssubstrate, UV ozone treatment was performed for 370 seconds afterwashing of a surface of the glass substrate with water and baking thatwas performed at 200° C. for 1 hour.

After that, the glass substrate was transferred into a vacuumevaporation apparatus where the pressure had been reduced toapproximately 10⁻⁴ Pa, and was subjected to vacuum baking at 170° C. for30 minutes in a heating chamber of the vacuum evaporation apparatus, andthen the glass substrate was cooled down for about 30 minutes.

Next, the glass substrate was fixed to a substrate holder in a vacuumevaporation apparatus so that a surface of the glass substrate on whichthe first electrode 2001 was formed faced downward. The pressure in thevacuum evaporation apparatus was reduced to about 10⁻⁴ Pa. Then,9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA) and molybdenum(VI) oxide were deposited on the first electrode2001 by co-evaporation to form a first hole-injection layer 2011. Thethickness thereof was 30 nm. The weight ratio of PCzPA to molybdenumoxide was adjusted to 2:1 (=PCzPA:molybdenum oxide).

Next, a BPAFLP film was formed to a thickness of 20 nm on thehole-injection layer 2011, whereby a hole-transport layer 2012 wasformed.

Next, 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-II),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) were co-deposited to form the firstlight-emitting layer 2013 a over the hole-transport layer 2012. Here,the weight ratio of 2mDBTPDBq-II (abbreviation) to PCBA1BP(abbreviation) and [Ir(tBuppm)₂(acac)] (abbreviation) was adjusted to0.7:0.3:0.06 (=2mDBTPDBq-II:PCBA1BP:[Ir(tBuppm)₂(acac)]). The thicknessof the first light-emitting layer 2013 a was set to 15 nm.

Next, 2mDBTPDBq-II, PCBA1BP, and [Ir(dppm)₂(acac)]) were deposited byco-evaporation, whereby the second light-emitting layer 2013 b wasformed over the first light-emitting layer 2013 a. Here, the weightratio of 2mDBTPDBq-II to PCBA1BP and [Ir(dppm)₂(acac)] was adjusted to0.7:0.3:0.06 (=2mDBTPDBq-II:PCBA1BP:[Ir(dppm)₂(acac)]). The thickness ofthe second light-emitting layer 2013 b was set to 15 nm.

Then, in order to form the third light-emitting layer 2013 c over thesecond light-emitting layer 2013 b, CzPA and 1,6 mMemFLAPAPrn weredeposited to a thickness of 10 nm by co-evaporation. The weight ratio ofCzPA to 1,6 mMemFLPAPrn was adjusted to 1:0.05 (=CzPA:1,6 mMemFLPAPrn).

Next, CzPA was vapor-deposited to a thickness of 5 nm and then BPhen wasvapor-deposited to a thickness of 15 nm, so that the electron-transportlayer 2014 was formed over the third light-emitting layer 2013 c.

Further, in order to form the electron-injection layer 2015 over theelectron-transport layer 2014, LiF was vapor-deposited to a thickness of1 nm.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 2003 functioning as a cathode. Thus,the light-emitting element 1 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 7 shows element structures of the light-emitting elements obtainedas described above in this example.

TABLE 7 Hole- Hole- Electron- Electron- 1st injection transport 1stlight- 2nd light- 3rd light- transport injection 2nd electrode layerlayer emitting layer emitting layer emitting layer layer layer electrodeITSO PCzPA: BPAFLP * CzPA: CzPA BPhen LiF Ag 110 nm MoOx 20 nm **1,6mMemFLPAPrn 5 nm 15 nm 1 nm 200 nm (=2:1) (=1:0.05) 30 nm 10 nm * 1stand 2nd light-emitting layers of 1st light-emitting device are asfollows. 1st light-emitting layer 2nd light-emitting layer2mDBTPDBq-II:PCBA1BP:[Ir(tBuppm)₂(acac)]2mDBTPDBq-II:PCBA1BP:[Ir(dppm)₂(acac)] (=0.7:0.3:0.06) (=0.7:0.3:0.06)15 nm 15 nm * 1st and 2nd light-emitting layers of 2nd light-emittingdevice are as follows. 1st light-emitting layer 2nd light-emitting layer2mDBTPDBq-II:PCBA1BP:[Ir(dppm)₂(acac)]2mDBTPDBq-II:PCBA1BP:[Ir(tBuppm)₂(acac)] (=0.7:0.3:0.06) (=0.7:0.3:0.06)15 nm 15 nm

Further, the light-emitting elements of this example were sealed in aglove box containing a nitrogen atmosphere so as not to be exposed tothe air (specifically, a sealant was applied onto outer edges of theelements and heat treatment was performed at 80° C. for 1 hour at thetime of sealing). Then, the operation characteristics of thelight-emitting elements of Example 3 were measured. Note that themeasurement was carried out at room temperature (in an atmosphere keptat 25° C.).

The initial values of the main characteristics of the light-emittingelement of this example at a luminance of 900 cd/m² are shown in Table8.

TABLE 8 Current Correlated Power External Volt- density Chroma- coloreffi- quantum age (mA/ ticity tempera- ciency effi- (V) cm²) (x, y) ture(K) (lm/W) ciency (%) Light- 2.8 1.3 (0.50, 0.49) 2800 76 21 emittingdevice 1 Light- 2.8 1.3 (0.53, 0.47) 2300 75 23 emitting device 2

The results show that light-emitting elements with favorablecharacteristics were obtained regardless of the order of forming thelight-emitting layer containing a green-light-emitting phosphorescentcompound and the light-emitting layer containing anorange-light-emitting phosphorescent compound.

Example 4

In this example, a technique will be described in which part ofcomponents of a light-emitting device is formed over a formationsubstrate and then the components are transferred from the formationsubstrate to a flexible substrate. This technique can be employed for amanufacturing method of a light-emitting device of one embodiment of thepresent invention.

<Manufacturing Method of Samples>

In order to manufacture samples 1 to 3 of this embodiment, part of themanufacturing method A (FIGS. 4A to 4E) of a light-emitting devicedescribed in Embodiment 3 was employed.

First, a 200-nm-thick silicon oxynitride film was formed as a base filmover a glass substrate serving as the formation substrate 601. Then,washing was performed using a hydrogen fluoride aqueous solution of0.5%.

Next, a 30-nm-thick tungsten film serving as the separation layer 603was formed over the base film. Then, nitrous oxide (N₂O) plasmatreatment was performed (conditions: gas (N₂O=100 sccm), power of 500 W,pressure of 100 Pa, substrate temperature of 330° C., 240 seconds).

Next, the layer 605 was formed over the separation layer 603. The layer605 in this example includes an insulating film. For the insulatingfilm, a silicon oxynitride film, a 200-nm-thick silicon nitride film, a200-nm-thick silicon oxynitride film, a 140-nm-thick silicon nitrideoxide film, and a 100-nm-thick silicon oxynitride film were stacked inthis order. Note that the thickness of the silicon oxynitride film incontact with the separation layer 603 was 200 nm in the sample 1 and 600nm in the samples 2 and 3.

After that, heat treatment was performed at 450° C. for 1 hour in anitrogen atmosphere.

A cross section of the sample 1 at this stage was observed with a STEM.It was found that, as shown in FIG. 19A, a tungsten oxide film wasformed between the tungsten film and the silicon oxynitride film.

Next, the layer 605 was bonded to the temporary supporting substrate607. A UV curable adhesive film (UV film) was used as the temporarysupporting substrate 607 of the sample 2. In the sample 3, a glasssubstrate was used as the temporary supporting substrate 607, and a UVcurable epoxy resin was used as the separation adhesive 609. Then, thelayer 605 was separated from the formation substrate 601 along theseparation layer 603. At this stage, the layer 605 was attached to thetemporary supporting substrate 607 side.

Next, cross sections of the samples 2 and 3 were observed with a STEM.FIG. 19B is a STEM image of the sample 2 on the formation substrate 601side. FIG. 19C is a STEM image of the sample 3 on the temporarysupporting substrate 607 side. As shown in FIGS. 19B and 19C, it wasfound that the tungsten film was separated from the silicon oxynitridefilm in the samples 2 and 3. More specifically, since the tungsten filmis present on the surface in FIG. 19B and the tungsten oxide film ispresent on the surface in FIG. 19C, it was found that the tungsten filmwas separated from the tungsten oxide film in each sample.

Example 5

In this example, a technique will be described in which part ofcomponents of a light-emitting device is formed over a formationsubstrate and then the components are transferred from the formationsubstrate to a flexible substrate. This technique can be employed for amanufacturing method of a light-emitting device of one embodiment of thepresent invention.

In the manufacturing method of the light-emitting device 7 of Example 2,the base film, the separation layer 603, and the layer 605 (including aninsulating film) were formed in this order over the formation substrate601. Similarly, in the manufacturing method of the samples in Example 4,the base film, the separation layer 603, and the layer 605 (including aninsulating film) were found in this order over the formation substrate601.

Specifically, a silicon oxynitride (first SiON) film was formed as thebase film; a tungsten (W) film was formed as the separation layer 603;and a silicon oxynitride (second SiON) film, a silicon nitride (SiN)film, a silicon oxynitride (third SiON) film, a silicon nitride oxide(SiNO) film, and a silicon oxynitride (first SiON) film were stacked inthis order as insulating films included in the layer 605.

In this example, single films corresponding to the above-described filmswere each formed on silicon substrates and stress values were measured.Note that stress values before and after heat treatment were measured inthis example. The heat treatment was performed in a nitrogen atmosphereat 450° C. for one hour.

Forming conditions of each film will be described. A 200-nm-thicksilicon oxynitride film was formed as the first SiON film. A 30-nm-thicktungsten film was formed as the W film. A 600-nm-thick siliconoxynitride film was fowled as the second SiON film. A 200-nm-thicksilicon nitride film was formed as the SiN film. A 200-nm-thick siliconoxynitride film was formed as the third SiON film. A 200-nm-thicksilicon oxynitride film was formed as the SiNO film.

Measurement results of stress values are shown in Table 9 and FIG. 20.

TABLE 9 Stress value [Mpa] Thickness before heat after heat Film [nm]treatment treatment Insulating film 1st SiON 200 −332 −160 SiNO 200 406870 3rd SiON 200 −187 −5.70 SiN 200 −554 −406 2nd SiON 600 −55.1 11.6Separation layer W 30 1150 77.0 Base film 1st SiON 200 −332 −156

It was found that the stress value of the W film which is a separationlayer was greatly decreased by the heat treatment. Further, it was foundthat the stress value of the second SiON film which is an insulatingfilm in contact with the separation layer was changed from positive tonegative by the heat treatment. The results in Example 4 show thatseparation occurs between the W film and the second SiON film when thelayer is separated from the formation substrate. Therefore, theseresults suggest that separation is easily caused in the film whosestress value is changed by the heat treatment (i.e., the stress value isgreatly decreased, the stress value is changed from positive tonegative, or the like).

Example 6

In Example 6, a light-emitting device which is one embodiment of thepresent invention is described. In this example, a bottom-emissionlight-emitting device was manufactured. FIG. 10D is a plan view of alight-emitting device 10 manufactured in this example. FIG. 21 is across-sectional view taken along dashed-dotted line X4-Y4 in FIG. 10D.Note that some components of the light-emitting device are omitted inFIG. 10D.

<Structure of Light-Emitting Device>

First, the structure of the light-emitting device 10 manufactured inthis example will be described. In the light-emitting device 10, thelight-emitting element 1250 is provided over a support 1229 with aninsulating film 1224 interposed therebetween. The area of alight-emitting region of the light-emitting element 1250 is 56 mm×42 mm.The auxiliary wiring 1206 is provided over the insulating film 1224 andis electrically connected to the first electrode 1201. The end portionof the first electrode 1201 and the end portion of the terminal 1210 arecovered with the partition wall 1205. Further, the partition wall 1205is provided to cover the auxiliary wiring 1206 with the first electrode1201 provided therebetween. The support 1229 and a sealing substrate1228 are bonded with a sealing material 1227. The support 1229 is apolyester-resin diffusion film and serves as a supporting substrate anda light extraction structure. The light-emitting device 10 is a flexiblelight-emitting device.

A specific structure of the light-emitting element 1250 included in thelight-emitting device 10 is shown in FIG. 18B. Example 2 can be referredto for the details of the structure of the light-emitting element 125.

<Manufacturing Method of Light-Emitting Device>

Next, a manufacturing method of the light-emitting device 10 isdescribed.

<Light-Emitting Device 10>

The light-emitting device 10 was manufactured in a manner similar tothat of the light-emitting device 7 except the EL layer 1202, theinsulating film 1224, and the support 1229; thus, description of stepssimilar to those in the light-emitting device 7 is omitted.

A manufacturing method of the EL layer 1202 in the light-emitting device10 will be described.

First, the supporting substrate 1200 over which the first electrode 1201was formed was fixed to a substrate holder provided in the vacuumevaporation apparatus so that the surface on which the first electrode1201 was formed faced downward. The pressure in the vacuum evaporationapparatus was reduced to about 10⁻⁴ Pa. After that, over the firstelectrode 1201, DBT3P-II and molybdenum oxide were deposited byco-evaporation by an evaporation method using resistance heating, sothat the hole-injection layer 1211 was formed over the first electrode1201. The thickness was 30 nm, and the weight ratio of DBT3P-II tomolybdenum oxide was adjusted to 2:1 (=DBT3P-II:molybdenum oxide).

Next, in order to form the hole-transport layer 1112 over thehole-injection layer 1111, BPAFLP and PCzPCN1 were deposited byco-evaporation to a thickness of 20 nm. The weight ratio of BPAFLP toPCzPCN1 was adjusted to 1:1 BPAFLP:PCzPCN1).

Further, a first light-emitting layer 1113 a was formed over thehole-transport layer 1112 by co-evaporation of 2mDBTBPDBq-II, PCzPCN1,and [Ir(tBuppm)₂(acac)]. Here, the weight ratio of 2mDBTBPDBq-II toPCzPCN1 and [Ir(tBuppm)₂(acac)] was adjusted to 0.7:0.3:0.06(=2mDBTBPDBq-II:PCzPCN1:[Ir(tBuppm)₂(acac)]). The thickness of the firstlight-emitting layer 1113 a was set to 12 nm.

Next, 2mDBTBPDBq-II, PCzPCN1, and [Ir(dppm)₂(acac)]) were deposited byco-evaporation, whereby the second light-emitting layer 1113 b wasformed over the first light-emitting layer 1113 a. Here, the weightratio of 2mDBTBPDBq-II, PCzPCN1, and [Ir(dppm)₂(acac)] was adjusted to0.8:0.2:0.06 (=2mDBTBPDBq-II:PCzPCN1:[Ir(dppm)₂(acac)]). In addition,the thickness of the second light-emitting layer 1113 b was set to 18nm.

Then, in order to form the third light-emitting layer 1113 c over thesecond light-emitting layer 1113 b, CzPA and 1,6mMemFLAPAPrn weredeposited to a thickness of 10 nm by co-evaporation. The weight ratio ofCzPA to 1,6 mMemFLPAPrn was adjusted to 1:0.05 (=CzPA:1,6 mMemFLPAPrn).

Next, CzPA was vapor-deposited to a thickness of 5 nm and then BPhen wasvapor-deposited to a thickness of 15 nm, so that the electron-transportlayer 1114 was formed over the third light-emitting layer 1113 c.

Further, in order to form the electron-injection layer 1215 over theelectron-transport layer 1214, LiF was vapor-deposited to a thickness of1 nm.

Finally, in order to form the second electrode 1203 serving as acathode, silver (Ag) and magnesium (Mg) were deposited to a thickness of1 nm by co-evaporation and further silver (Ag) was vapor-deposited to athickness of 250 nm. Here, the volume ratio of Ag to Mg was adjusted to1:0.3 (=Ag:Mg).

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 10 shows element structure of the light-emitting elementmanufactured as described above.

TABLE 10 Hole- Hole- Electron- Electron- 1st injection transport 1stlight- 2nd light- 3rd light- transport injection 2nd electrode layerlayer emitting layer emitting layer emitting layer layer layer electrodeITSO DBT3P-II: BPAFLP: 2mDBTBPDBq-II: 2mDBTBPDBq-II: CzPA: CzPA BPhenLiF Ag:Mg Ag 110 nm MoOx PCzPCN1 PCzPCN1: PCzPCN1: 1,6mMemFLPAPrn 5 nm15 nm 1 nm (=1:0.3) 250 nm (=2:1) (=1:1) [Ir(tBuppm)₂(acac)][Ir(dppm)₂(acac)] (=1:0.05) 1 nm 30 nm 20 nm (=0.7:0.3:0.06)(=0.8:0.2:0.06) 10 nm 12 nm 18 nm

For the insulating film 1224 in the light-emitting device 10, a600-nm-thick silicon oxynitride film, a 100-nm-thick silicon nitridefilm, and a 150-nm-thick silicon oxynitride film were stacked in thisorder.

In the light-emitting device 10, the layer 605 which was separated fromthe formation substrate 601 and includes the exposed insulating film1224 was bonded to the support 1229 using a UV curable adhesive.

<Characteristics of Light-Emitting Device>

Table 11 shows initial values of main characteristics of thelight-emitting device 10 at a current density of 0.81 mA/cm².

TABLE 11 Correlated External color Power quantum Voltage Chromaticitytemperature efficiency efficiency (V) (x, y) (K) (lm/W) (%) Light- 2.63(0.49, 0.50) 3000 131 34 emitting device 10

In the light-emitting element of this example, the green-light-emittingphosphorescent compound, the orange-light-emitting phosphorescentcompound, and the blue-light-emitting fluorescent compound were used aslight-emitting substances. Adjustment of emission balance among thephosphorescent and fluorescent light-emitting layers could increaseemission efficiency of the light-emitting element.

In the light-emitting element of this example, the electron-transportorganic compound is used as a host material of the blue-light-emittingfluorescent compound and is positioned to be the closest to the cathodeamong the three light-emitting layers; with this structure, lightemission from the phosphorescent compounds is easily obtained.Accordingly, the light-emitting element with high emission efficiencywas achieved.

Although light emitted from a fluorescent compound is weaker than thatfrom a phosphorescent compound, the light-emitting element of thisexample is preferable particularly in the case where a strong blueemission is unnecessary and high emission efficiency is required, forexample, for a warm-white light-emitting device used as lighting.

The power efficiency of the light-emitting device 10 at a currentdensity of 0.81 mA/cm² was 131 lm/W and the voltage was 2.63 V. On theother hand, the power efficiency of the light-emitting device 7 ofExample 2 at a current density of 0.90 mA/cm² was 1091 lm/W and thevoltage was 2.95 V. From these results, it was found that thelight-emitting device 10 had lower driving voltage and higher efficiencythan the light-emitting device 7. Since a light-emitting element capableof forming an exciplex is used in the light-emitting device 10, thedriving voltage is low. Further, the light-emitting device 10 includesthe insulating film 1224 whose structure is different from that of thelight-emitting device 7. In addition, the light-emitting device 10 doesnot include the supporting substrate 1220 and a UV curable epoxy resinfor bonding the light extraction structure 1209 to the supportingsubstrate 1220, and instead include the support 1229. For these reasons,the light extraction efficiency is improved and thus the powerefficiency is high.

This application is based on Japanese Patent Application serial No.2012-261011 filed with Japan Patent Office on Nov. 29, 2012, JapanesePatent Application serial No. 2012-264071 filed with Japan Patent Officeon Dec. 3, 2012, and Japanese Patent Application serial No. 2013-043643filed with Japan Patent Office on Mar. 6, 2013, the entire contents ofwhich are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting device comprising: a firstelectrode; a hole-transport layer over the first electrode, thehole-transport layer comprising a first organic compound; a firstlight-emitting layer over the hole-transport layer, the firstlight-emitting layer comprising a first phosphorescent compound which isconfigured to emit one of green light or orange light and a secondorganic compound; a second light-emitting layer over the firstlight-emitting layer, the second light-emitting layer comprising asecond phosphorescent compound which is configured to emit the other ofgreen light or orange light and a third organic compound; a thirdlight-emitting layer over the second light-emitting layer, the thirdlight-emitting layer comprising a fluorescent compound which isconfigured to emit blue light and a fourth organic compound; anelectron-transport layer over the third light-emitting layer, theelectron-transport layer comprising a fifth organic compound; and asecond electrode over the electron-transport layer.
 2. Thelight-emitting device according to claim 1, wherein the second organiccompound is the same compound as at least one of the first organiccompound and the third organic compound.
 3. The light-emitting deviceaccording to claim 1, wherein the fourth organic compound is the samecompound as the fifth organic compound.
 4. The light-emitting deviceaccording to claim 1, wherein the second organic compound is the samecompound as at least one of the first organic compound and the thirdorganic compound, and wherein the fourth organic compound is the samecompound as the fifth organic compound.
 5. The light-emitting deviceaccording to claim 1, wherein the fluorescent compound comprises apyrene skeleton.
 6. The light-emitting device according to claim 1,wherein at least one of the fourth organic compound and the fifthorganic compound comprises an anthracene skeleton.
 7. The light-emittingdevice according to claim 1, wherein the light-emitting device isconfigured to emit yellow light.
 8. An electronic device comprising thelight-emitting device according to claim
 1. 9. A lighting devicecomprising the light-emitting device according to claim
 1. 10. Alight-emitting device comprising: a first electrode; a hole-injectionlayer over the first electrode, the hole-injection layer comprising ahole-injection substance; a hole-transport layer over the hole-injectionlayer, the hole-transport layer comprising a first organic compound; afirst light-emitting layer over the hole-transport layer, the firstlight-emitting layer comprising a first phosphorescent compound which isconfigured to emit one of green light or orange light and a secondorganic compound; a second light-emitting layer over the firstlight-emitting layer, the second light-emitting layer comprising asecond phosphorescent compound which is configured to emit the other ofgreen light or orange light and a third organic compound; a thirdlight-emitting layer over the second light-emitting layer, the thirdlight-emitting layer comprising a fluorescent compound which isconfigured to emit blue light and a fourth organic compound; anelectron-transport layer over the third light-emitting layer, theelectron-transport layer comprising a fifth organic compound; anelectron-injection layer over the electron-transport layer, theelectron-injection layer comprising an electron-injection substance; anda second electrode over the electron-injection layer.
 11. Thelight-emitting device according to claim 10, wherein the second organiccompound is the same compound as at least one of the first organiccompound and the third organic compound.
 12. The light-emitting deviceaccording to claim 10, wherein the fourth organic compound is the samecompound as the fifth organic compound.
 13. The light-emitting deviceaccording to claim 10, wherein the second organic compound is the samecompound as at least one of the first organic compound and the thirdorganic compound, and wherein the fourth organic compound is the samecompound as the fifth organic compound.
 14. The light-emitting deviceaccording to claim 10, wherein the fluorescent compound comprises apyrene skeleton.
 15. The light-emitting device according to claim 10,wherein at least one of the fourth organic compound and the fifthorganic compound comprises an anthracene skeleton.
 16. Thelight-emitting device according to claim 10, wherein the light-emittingdevice is configured to emit yellow light.
 17. The light-emitting deviceaccording to claim 10, wherein at least one of the hole-injection layerand the electron-injection layer comprises a charge-generation region.18. An electronic device comprising the light-emitting device accordingto claim
 10. 19. A lighting device comprising the light-emitting deviceaccording to claim 10.